cmd/go: delete unused function isInGoToolsRepo
cmd/go: delete unused function isInGoToolsRepo

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/66350
Reviewed-by: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
Run-TryBot: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

polyverse-security/go,golang/go,Cofyc/go,cloudflare/go,codestation/go,polyverse-security/go,akutz/go,nawawi/go,akutz/go,cloudflare/go,josharian/go,akutz/go,codestation/go,josharian/go,akutz/go,Cofyc/go,akutz/go,CAFxX/go,akutz/go,polyverse-security/go,golang/go,christopher-henderson/Go,josharian/go,cloudflare/go,codestation/go,CAFxX/go,CAFxX/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,akutz/go,Cofyc/go,josharian/go,Cofyc/go,polyverse-security/go,CAFxX/go,nawawi/go,golang/go,cloudflare/go,codestation/go,nawawi/go,polyverse-security/go,CAFxX/go,Cofyc/go,golang/go,golang/go,nawawi/go,polyverse-security/go,codestation/go,josharian/go,nawawi/go,josharian/go,cloudflare/go,CAFxX/go,polyverse-security/go,golang/go,polyverse-security/go,akutz/go,cloudflare/go,Cofyc/go,Cofyc/go,codestation/go,golang/go,Cofyc/go,nawawi/go,josharian/go,cloudflare/go,josharian/go,codestation/go,cloudflare/go,codestation/go,CAFxX/go