go,internal,io,mime: use slices and maps to clean tests
Replace reflect.DeepEqual with slices.Equal/maps.Equal, which is
much faster.
Change-Id: Id9cb550884da817da96befdeccfecb3325fb4414
GitHub-Last-Rev:
7d64d78feb86e3ea1af6c24ea6782cb85731bb52
GitHub-Pull-Request: golang/go#67612
Reviewed-on: https://go-review.googlesource.com/c/go/+/587819
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>