The function isInGoToolsRepo has no use case anymore, so we remove it
with this change.

Change-Id: I71051828eef2e317b83e13f83a14d5f0bc0ec13f
Reviewed-on: https://go-review.googlesource.com/66350Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>