[build] Remove extra_headers from sdk_{source_set,static_library}

This GN template parameter was introduced to deal with the issue
described in the associated bug, which has since been fixed by
adding all required explicit dependencies where they were needed.

The parameter and its use can now be safely removed.

For testing, the content of out/default/sdk/archive/core.tar.gz
was compared before/after this CL was applied to verify that they
are identical.

Fixed: 60129
Change-Id: Ide951c0f1ed96d10e16276d61c29f7a790916bf6
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/560821
Reviewed-by: Jay Zhuang <jayzhuang@google.com>
Reviewed-by: David Fang <fangism@google.com>
Commit-Queue: David Turner <digit@google.com>
diff --git a/build/cpp/sdk_source_set.gni b/build/cpp/sdk_source_set.gni
index b0805b7..e259dc9 100644
--- a/build/cpp/sdk_source_set.gni
+++ b/build/cpp/sdk_source_set.gni
@@ -44,11 +44,6 @@
 #     List of dependencies that should not be reflected in SDKs.
 #     Mostly useful for code generation.
 #
-#   extra_headers [optional]
-#     List of header files that are part of the SDK headers for the library
-#     but that must not be exposed as part of the Fuchsia build. This must ONLY
-#     be used as a work-around for https://fxbug.dev/60129.
-#
 template("sdk_source_set") {
   assert(defined(invoker.category), "Must define an SDK category")
   assert(defined(invoker.sdk_name), "Must define an SDK name")
@@ -134,9 +129,6 @@
   } else {
     not_needed([ "source_headers_are_public" ])
   }
-  if (defined(invoker.extra_headers)) {
-    all_headers += invoker.extra_headers
-  }
 
   # Determine destinations in the SDK for headers and sources.
   file_base = "pkg/${invoker.sdk_name}"
diff --git a/build/cpp/sdk_static_library.gni b/build/cpp/sdk_static_library.gni
index 1aeb0ec..5b8c5527 100644
--- a/build/cpp/sdk_static_library.gni
+++ b/build/cpp/sdk_static_library.gni
@@ -39,11 +39,6 @@
 #     List of labels representing the library's runtime dependencies. This is
 #     only needed for runtime dependencies inherited from private dependencies.
 #     Note that these labels should represent SDK targets.
-#
-#   extra_headers [optional]
-#     List of header files that are part of the SDK headers for the library
-#     but that must not be exposed as part of the Fuchsia build. This must ONLY
-#     be used to work-around for https://fxbug.dev/60129.
 
 # The defaults for a sdk_static_library should match that of a shared_library.
 set_defaults("sdk_static_library") {
@@ -187,9 +182,6 @@
       }
     }
   }
-  if (defined(invoker.extra_headers)) {
-    all_headers += invoker.extra_headers
-  }
   assert(all_headers != [], "Library does not contain any headers or sources.")
   sdk_metadata_headers = []
   sdk_header_files = []
diff --git a/build/unification/zx_library.gni b/build/unification/zx_library.gni
index bb24cf0..55898d0 100644
--- a/build/unification/zx_library.gni
+++ b/build/unification/zx_library.gni
@@ -333,12 +333,6 @@
         foreach(header, invoker.sdk_headers) {
           public += [ "include/$header" ]
         }
-      } else if (defined(invoker.sdk_headers) && sdkable) {
-        # Add the headers to `sources` to ensure sdk_atom checks the API properly.
-        extra_headers = []
-        foreach(header, invoker.sdk_headers) {
-          extra_headers += [ "include/$header" ]
-        }
       }
 
       if (!defined(public_configs)) {