Revert "Update dependency com_github_grpc_grpc to v1.24.2 (#7)" (#10)
Revert "Update dependency com_github_grpc_grpc to v1.24.2 (#7)" (#10)

The original change breaks the build.
googleapis/google-cloud-cpp-bigquery,googleapis/google-cloud-cpp-bigquery,googleapis/google-cloud-cpp-bigquery,googleapis/google-cloud-cpp-bigquery