all: clean unnecessary casts for test files
This is a follow up of CL 528696.
Change-Id: I5b71eabedb12567c4b1b36f7182a3d2b0ed662a5
GitHub-Last-Rev:
acaf3ac11c38042ad27b99e1c70a3c9f1a554a15
GitHub-Pull-Request: golang/go#62713
Reviewed-on: https://go-review.googlesource.com/c/go/+/529197
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>