testing(bigquery): remove header check enforcement for secondary APIs (googleapis#13381)

Changes to underlying structure of the dial pattern have complicated
testing slightly. This PR removes header check enforcement from the
secondary APIs BQ integration testing uses, as they're not really
evaluating the client under test.

Fixes: googleapis#13373

Author: shollyman

bigquery/integration_test.go

@@ -206,9 +206,6 @@ func initIntegrationTest() func() {
 			// We can't check universally because option.WithHTTPClient is
 			// incompatible with gRPC options.
 			bqOpts = append(bqOpts, grpcHeadersChecker.CallOptions()...)
-			sOpts = append(sOpts, grpcHeadersChecker.CallOptions()...)
-			ptmOpts = append(ptmOpts, grpcHeadersChecker.CallOptions()...)
-			connOpts = append(connOpts, grpcHeadersChecker.CallOptions()...)
 		}
 		var err error
 		client, err = NewClient(ctx, projID, bqOpts...)