Remove deleted files from Makefile.am.

Makefile.am

@@ -195,7 +195,6 @@ python_EXTRA_DIST=                                                           \
   python/google/protobuf/internal/wire_format.py                             \
   python/google/protobuf/internal/wire_format_test.py                        \
   python/google/protobuf/internal/__init__.py                                \
-  python/google/protobuf/internal/import_test_package/BUILD                  \
   python/google/protobuf/internal/import_test_package/__init__.py            \
   python/google/protobuf/internal/import_test_package/inner.proto            \
   python/google/protobuf/internal/import_test_package/outer.proto            \