Remove AstroidCacheSetupMixin

This class predates efforts to have a central interface to control
global state (including caches) and it is no longer needed.
diff --git a/astroid/interpreter/_import/spec.py b/astroid/interpreter/_import/spec.py
index e1c5ed0..77351c2 100644
--- a/astroid/interpreter/_import/spec.py
+++ b/astroid/interpreter/_import/spec.py
@@ -474,7 +474,3 @@
             spec = spec._replace(submodule_search_locations=submodule_path)
 
     return spec
-
-
-def clear_spec_cache() -> None:
-    _find_spec.cache_clear()
diff --git a/astroid/manager.py b/astroid/manager.py
index 195ac66..fc30bf9 100644
--- a/astroid/manager.py
+++ b/astroid/manager.py
@@ -442,12 +442,11 @@
         # pylint: disable=import-outside-toplevel
         from astroid.brain.helpers import register_all_brains
         from astroid.inference_tip import clear_inference_tip_cache
-        from astroid.interpreter._import.spec import clear_spec_cache
+        from astroid.interpreter._import.spec import _find_spec
         from astroid.interpreter.objectmodel import ObjectModel
         from astroid.nodes._base_nodes import LookupMixIn
         from astroid.nodes.scoped_nodes import ClassDef
 
-        clear_spec_cache()
         clear_inference_tip_cache()
         _invalidate_cache()  # inference context cache
 
@@ -461,6 +460,7 @@
             util.is_namespace,
             ObjectModel.attributes,
             ClassDef._metaclass_lookup_attribute,
+            _find_spec,
         ):
             lru_cache.cache_clear()  # type: ignore[attr-defined]
 
diff --git a/tests/resources.py b/tests/resources.py
index 455dc6f..853fd79 100644
--- a/tests/resources.py
+++ b/tests/resources.py
@@ -9,7 +9,6 @@
 from pathlib import Path
 
 from astroid import builder
-from astroid.manager import AstroidManager
 from astroid.nodes.scoped_nodes import Module
 
 DATA_DIR = Path("testdata") / "python3"
@@ -34,28 +33,3 @@
         for key in list(sys.path_importer_cache):
             if key.startswith(datadir):
                 del sys.path_importer_cache[key]
-
-
-class AstroidCacheSetupMixin:
-    """Mixin for handling test isolation issues with the astroid cache.
-
-    When clearing the astroid cache, some tests fail due to
-    cache inconsistencies, where some objects had a different
-    builtins object referenced.
-    This saves the builtins module and TransformVisitor and
-    replaces them after the tests finish.
-    The builtins module is special, since some of the
-    transforms for a couple of its objects (str, bytes etc)
-    are executed only once, so astroid_bootstrapping will be
-    useless for retrieving the original builtins module.
-    """
-
-    @classmethod
-    def setup_class(cls):
-        cls._builtins = AstroidManager().astroid_cache.get("builtins")
-        cls._transforms = AstroidManager.brain["_transform"]
-
-    @classmethod
-    def teardown_class(cls):
-        AstroidManager().astroid_cache["builtins"] = cls._builtins
-        AstroidManager.brain["_transform"] = cls._transforms
diff --git a/tests/test_manager.py b/tests/test_manager.py
index 160fa94..c91ec0a 100644
--- a/tests/test_manager.py
+++ b/tests/test_manager.py
@@ -23,7 +23,6 @@
     AttributeInferenceError,
 )
 from astroid.interpreter._import import util
-from astroid.interpreter._import.spec import clear_spec_cache
 from astroid.modutils import EXT_LIB_DIRS, module_in_path
 from astroid.nodes import Const
 from astroid.nodes.scoped_nodes import ClassDef, Module
@@ -37,13 +36,11 @@
     return obj.__file__
 
 
-class AstroidManagerTest(
-    resources.SysPathSetup, resources.AstroidCacheSetupMixin, unittest.TestCase
-):
+class AstroidManagerTest(resources.SysPathSetup, unittest.TestCase):
     def setUp(self) -> None:
         super().setUp()
-        clear_spec_cache()
         self.manager = test_utils.brainless_manager()
+        self.manager.clear_cache()
 
     def test_ast_from_file(self) -> None:
         filepath = unittest.__file__
@@ -393,9 +390,10 @@
         self.manager.ast_from_module_name("math")
 
 
-class IsolatedAstroidManagerTest(resources.AstroidCacheSetupMixin, unittest.TestCase):
+class IsolatedAstroidManagerTest(unittest.TestCase):
     def test_no_user_warning(self):
         mgr = manager.AstroidManager()
+        self.addCleanup(mgr.clear_cache)
         with warnings.catch_warnings():
             warnings.filterwarnings("error", category=UserWarning)
             mgr.ast_from_module_name("setuptools")
diff --git a/tests/test_modutils.py b/tests/test_modutils.py
index be7095e..7921757 100644
--- a/tests/test_modutils.py
+++ b/tests/test_modutils.py
@@ -22,7 +22,6 @@
 from astroid import modutils
 from astroid.const import PY310_PLUS
 from astroid.interpreter._import import spec
-from astroid.interpreter._import.spec import clear_spec_cache
 
 from . import resources
 
@@ -42,7 +41,7 @@
     package = "mypypa"
 
     def tearDown(self) -> None:
-        clear_spec_cache()
+        astroid.MANAGER.clear_cache()
         for k in list(sys.path_importer_cache):
             if "MyPyPa" in k:
                 del sys.path_importer_cache[k]
diff --git a/tests/test_regrtest.py b/tests/test_regrtest.py
index 67ccca6..45f241f 100644
--- a/tests/test_regrtest.py
+++ b/tests/test_regrtest.py
@@ -26,10 +26,11 @@
     HAS_NUMPY = True
 
 
-class NonRegressionTests(resources.AstroidCacheSetupMixin, unittest.TestCase):
+class NonRegressionTests(unittest.TestCase):
     def setUp(self) -> None:
         sys.path.insert(0, resources.find("data"))
         MANAGER.always_load_extensions = True
+        self.addCleanup(MANAGER.clear_cache)
 
     def tearDown(self) -> None:
         MANAGER.always_load_extensions = False