fix(hermetic_build): keep only grpc-gcp-java in module allowlist

Author: blakeli0

sdk-platform-java/hermetic_build/library_generation/utils/pom_generator.py

@@ -72,7 +72,6 @@ def get_version_from(
         "google-auth-library-java",
         "sdk-platform-java",
         "java-showcase",
-        "grpc-gcp",
         "grpc-gcp-java",
     ]
 )