FR: Drop `grpc-java` `bazel_dep` as it interferes with `maven` workspace

While the `grpc-java` dep is currently needed for the gazelle plugin, it interferes with the default `maven` namespace, and this is by design. However, users of `contrib_rules_jvm` complain about this. Rather than try and change `grpc-java` in a patch that won't be accepted, it would be cleaner for us to drop the dependency and use something else.