Breaking change: Remove deprecated py_proto_library macro.

This has been replaced with a much better implementation in rules_python, that will be moved to the protobuf repo in 29.0

PiperOrigin-RevId: 691141509

protobuf.bzl

@@ -576,9 +576,9 @@ def internal_py_proto_library(
         **kargs):
     """Bazel rule to create a Python protobuf library from proto source files
 
-    NOTE: the rule is only an internal workaround to generate protos. The
-    interface may change and the rule may be removed when bazel has introduced
-    the native rule.
+    NOTE: the rule is is only an internal workaround to generate protos.  It is deprecated and will
+    be removed in the next minor release.  Users should migrate to the py_proto_library rule from
+    rules_python instead.
 
     Args:
       name: the name of the py_proto_library.
@@ -638,21 +638,6 @@ def internal_py_proto_library(
         **kargs
     )
 
-def py_proto_library(
-        *args,
-        **kwargs):
-    """Deprecated alias for use before Bazel 5.3.
-
-    Args:
-      *args: the name of the py_proto_library.
-      **kwargs: other keyword arguments that are passed to py_library.
-
-    Deprecated:
-      This is provided for backwards compatibility only.  Bazel 5.3 will
-      introduce support for py_proto_library, which should be used instead.
-    """
-    internal_py_proto_library(*args, **kwargs)
-
 def _source_proto_library(
         name,
         srcs = [],