Revert "[reflection] python: reflection response returns dependencies" (#33088)

Reverts grpc/grpc#32909

It's breaking some internal test
(//net/grpc/python:internal_tests/unit/_default_reflection_test), revert
for now to investigate.

src/python/grpcio_reflection/grpc_reflection/v1alpha/_base.py

@@ -30,29 +30,13 @@ def _not_found_error():
         ))
 
 
-def _collect_transitive_dependencies(descriptor, seen_files):
-    seen_files.update({descriptor.name: descriptor})
-    for dependency in descriptor.dependencies:
-        if not dependency.name in seen_files:
-            # descriptors cannot have circular dependencies
-            _collect_transitive_dependencies(dependency, seen_files)
-
-
 def _file_descriptor_response(descriptor):
-    # collect all dependencies
-    descriptors = {}
-    _collect_transitive_dependencies(descriptor, descriptors)
-
-    # serialize all descriptors
-    serialized_proto_list = []
-    for d_key in descriptors:
     proto = descriptor_pb2.FileDescriptorProto()
-        descriptors[d_key].CopyToProto(proto)
-        serialized_proto_list.append(proto.SerializeToString())
-
+    descriptor.CopyToProto(proto)
+    serialized_proto = proto.SerializeToString()
     return _reflection_pb2.ServerReflectionResponse(
         file_descriptor_response=_reflection_pb2.FileDescriptorResponse(
-            file_descriptor_proto=(serialized_proto_list)),)
+            file_descriptor_proto=(serialized_proto,)),)
 
 
 class BaseReflectionServicer(_reflection_pb2_grpc.ServerReflectionServicer):

src/python/grpcio_tests/tests/reflection/_reflection_servicer_test.py

@@ -25,7 +25,6 @@ from grpc_reflection.v1alpha import reflection_pb2_grpc
 
 from src.proto.grpc.testing import empty_pb2
 from src.proto.grpc.testing.proto2 import empty2_extensions_pb2
-from src.proto.grpc.testing.proto2 import empty2_pb2
 from tests.unit import test_common
 
 _EMPTY_PROTO_FILE_NAME = 'src/proto/grpc/testing/empty.proto'
@@ -129,11 +128,9 @@ class ReflectionServicerTest(unittest.TestCase):
         expected_responses = (
             reflection_pb2.ServerReflectionResponse(
                 valid_host='',
-                file_descriptor_response=reflection_pb2.
-                FileDescriptorResponse(file_descriptor_proto=(
-                    _file_descriptor_to_proto(empty2_extensions_pb2.DESCRIPTOR),
-                    _file_descriptor_to_proto(empty2_pb2.DESCRIPTOR),
-                ))),
+                file_descriptor_response=reflection_pb2.FileDescriptorResponse(
+                    file_descriptor_proto=(_file_descriptor_to_proto(
+                        empty2_extensions_pb2.DESCRIPTOR),))),
             reflection_pb2.ServerReflectionResponse(
                 valid_host='',
                 error_response=reflection_pb2.ErrorResponse(

src/python/grpcio_tests/tests_aio/reflection/reflection_servicer_test.py

@@ -25,7 +25,6 @@ from grpc_reflection.v1alpha import reflection_pb2_grpc
 
 from src.proto.grpc.testing import empty_pb2
 from src.proto.grpc.testing.proto2 import empty2_extensions_pb2
-from src.proto.grpc.testing.proto2 import empty2_pb2
 from tests_aio.unit._test_base import AioTestBase
 
 _EMPTY_PROTO_FILE_NAME = 'src/proto/grpc/testing/empty.proto'
@@ -133,11 +132,9 @@ class ReflectionServicerTest(AioTestBase):
         expected_responses = (
             reflection_pb2.ServerReflectionResponse(
                 valid_host='',
-                file_descriptor_response=reflection_pb2.
-                FileDescriptorResponse(file_descriptor_proto=(
-                    _file_descriptor_to_proto(empty2_extensions_pb2.DESCRIPTOR),
-                    _file_descriptor_to_proto(empty2_pb2.DESCRIPTOR),
-                ))),
+                file_descriptor_response=reflection_pb2.FileDescriptorResponse(
+                    file_descriptor_proto=(_file_descriptor_to_proto(
+                        empty2_extensions_pb2.DESCRIPTOR),))),
             reflection_pb2.ServerReflectionResponse(
                 valid_host='',
                 error_response=reflection_pb2.ErrorResponse(