cmd/go/internal: use strings.CutSuffix
Updates #42537
Change-Id: I2d4c5e911c8a2ddfe9a976896b05d3cd8be61f6b
GitHub-Last-Rev:
a87597d8a7a84c4975fb5e13004feda9b6abce34
GitHub-Pull-Request: golang/go#55830
Reviewed-on: https://go-review.googlesource.com/c/go/+/433275
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>