cmd/go: replace the 'addcrlf' script command with a more general 'replace' command

cmd/go: replace the 'addcrlf' script command with a more general 'replace' command

This allows the "reuse_git" test to avoid depending on exact JSON
blobs, which will be important when the URLs start referring to
test-local vcweb servers.

For #27494.

Change-Id: I22fde5110b3267b8fb9fb9c59fabc3b8a8b492c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/427094
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>