avoid unused variable error
avoid unused variable error

motivation:
[...]/internal.pb.go:16323]: __go_fuzz_tmp declared and not used

the source is in cockroachdb/cockroach/proto/internal.pb.go
and is a switch statement with only the default case.

dvyukov/go-fuzz,octo/go-fuzz,octo/go-fuzz,dvyukov/go-fuzz