strings: delete unused constant
strings: delete unused constant

Change-Id: I235c5bc7ce598047eccc1518984dd27f568046a2
Reviewed-on: https://go-review.googlesource.com/82776
Run-TryBot: Caleb Spare <dce7183dd721072d236fed9264529050987c94bf@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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