Remove the rec argument from 'find_argname' as promised

The `rec` parameter and `DEPRECATED_ARGUMENT_DEFAULT` sentinel were
deprecated since astroid 3.1. Remove them now that we're on 4.2.

astroid/nodes/node_classes.py

diff --git a/astroid/nodes/node_classes.py b/astroid/nodes/node_classes.py
index 144f2f8..2e1e3a6 100644
--- a/astroid/nodes/node_classes.py
+++ b/astroid/nodes/node_classes.py
@@ -597,9 +597,6 @@
         return _infer_stmts(stmts, context, frame)
 
 
-DEPRECATED_ARGUMENT_DEFAULT = "DEPRECATED_ARGUMENT_DEFAULT"
-
-
 class Arguments(
     _base_nodes.AssignTypeNode
 ):  # pylint: disable=too-many-instance-attributes
@@ -969,7 +966,7 @@
             return True
         return self.find_argname(name)[1] is not None
 
-    def find_argname(self, argname, rec=DEPRECATED_ARGUMENT_DEFAULT):
+    def find_argname(self, argname):
         """Get the index and :class:`AssignName` node for given name.
 
         :param argname: The name of the argument to search for.
@@ -978,12 +975,6 @@
         :returns: The index and node for the argument.
         :rtype: tuple(str or None, AssignName or None)
         """
-        if rec != DEPRECATED_ARGUMENT_DEFAULT:  # pragma: no cover
-            warnings.warn(
-                "The rec argument will be removed in astroid 3.1.",
-                DeprecationWarning,
-                stacklevel=2,
-            )
         if self.arguments:
             index, argument = _find_arg(argname, self.arguments)
             if argument: