cmd/compile/internal/types2: use internal/types/errors instead of local error codes

cmd/compile/internal/types2: use internal/types/errors instead of local error codes

Change-Id: If9b5c2c5d1b89146250bcd19965797baab315876
Reviewed-on: https://go-review.googlesource.com/c/go/+/439564
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>