inline bounded external:protocol_compiler (#36262)

Related to #36157

This is only focused on one binding so it is validated progressively

Closes #36262

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36262 from mmorel-35:externalprotocol_compiler f00cce8728
PiperOrigin-RevId: 639101071

bazel/generate_cc.bzl

@@ -187,7 +187,7 @@ _generate_cc = rule(
             mandatory = False,
         ),
         "_protoc": attr.label(
-            default = Label("//external:protocol_compiler"),
+            default = Label("@com_google_protobuf//:protoc"),
             executable = True,
             cfg = "exec",
         ),

bazel/generate_objc.bzl

@@ -180,7 +180,7 @@ generate_objc = rule(
             default = "@com_google_protobuf//:well_known_type_protos",
         ),
         "_protoc": attr.label(
-            default = Label("//external:protocol_compiler"),
+            default = Label("@com_google_protobuf//:protoc"),
             executable = True,
             cfg = "exec",
         ),

bazel/python_rules.bzl

@@ -110,7 +110,7 @@ _gen_py_aspect = aspect(
     fragments = ["py"],
     attrs = {
         "_protoc": attr.label(
-            default = Label("//external:protocol_compiler"),
+            default = Label("@com_google_protobuf//:protoc"),
             providers = ["files_to_run"],
             executable = True,
             cfg = "exec",
@@ -166,7 +166,7 @@ py_proto_library = rule(
             aspects = [_gen_py_aspect],
         ),
         "_protoc": attr.label(
-            default = Label("//external:protocol_compiler"),
+            default = Label("@com_google_protobuf//:protoc"),
             providers = ["files_to_run"],
             executable = True,
             cfg = "exec",
@@ -259,7 +259,7 @@ _generate_pb2_grpc_src = rule(
             executable = True,
             providers = ["files_to_run"],
             cfg = "exec",
-            default = Label("//external:protocol_compiler"),
+            default = Label("@com_google_protobuf//:protoc"),
         ),
         "grpc_library": attr.label(
             default = Label("//src/python/grpcio/grpc:grpcio"),