all: omit unnecessary type conversions
Found by github.com/mdempsky/unconvert
Change-Id: Ib78cceb718146509d96dbb6da87b27dbaeba1306
GitHub-Last-Rev:
dedf354811701ce8920c305b6f7aa78914a4171c
GitHub-Pull-Request: golang/go#74771
Reviewed-on: https://go-review.googlesource.com/c/go/+/690735
Reviewed-by: Mark Freeman <mark@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>