Update to Go 1.12.5 testing. Remove deprecated unused and gosimple
pacakges, and mask staticcheck 1006. Also, fix unconvert errors related
to unnecessary type conversions and following staticcheck errors:
- remove redundant return statements
- use for range instead of for select
- use time.Since instead of time.Now().Sub
- omit comparison to bool constant
- replace T.Fatal and T.Fatalf in tests with T.Error and T.Fatalf respectively because the goroutine calls T.Fatal must be called in the same goroutine as the test
- fix error strings that should not be capitalized
- use sort.Strings(...) instead of sort.Sort(sort.StringSlice(...))
- use he status code of Canceled instead of grpc.ErrClientConnClosing which is deprecated
- use use status.Errorf instead of grpc.Errorf which is deprecated
Related #10528#10438
