chore(storage): delete and migrate grpc specific tests (#6853)

Some previously added gRPC media operation integration tests are now covered by the well established JSON via the `multiTransportTest` helper. This removes several of those now redundant gRPC-specific tests.

It also "migrates" a few gRPC-specific tests that we'd like to keep and updates them to use more regular testing helpers. These are necessary to exercise transport-specific specific scenarios with regards to stream management.