api: remove testing Context accessors from go1.8.txt
api: remove testing Context accessors from go1.8.txt

Fixes the build.

Updates #18199

Change-Id: Ibf029ba9f9293d1f3d49c1c8773fc262159a5d5b
Reviewed-on: https://go-review.googlesource.com/34242
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

josharian/go,vsekhar/elastic-go,Cofyc/go,nawawi/go,cloudflare/go,cloudflare/go,polyverse-security/go,polyverse-security/go,vsekhar/elastic-go,suncycheng/go,vsekhar/elastic-go,polyverse-security/go,Cofyc/go,cloudflare/go,ImJasonH/go,ImJasonH/go,vsekhar/elastic-go,linux-on-ibm-z/go,ImJasonH/go,linux-on-ibm-z/go,golang/go,linux-on-ibm-z/go,Cofyc/go,polyverse-security/go,nawawi/go,golang/go,suncycheng/go,CAFxX/go,cloudflare/go,josharian/go,josharian/go,golang/go,cloudflare/go,cloudflare/go,derekmarcotte/go,codestation/go,nawawi/go,Cofyc/go,polyverse-security/go,akutz/go,josharian/go,akutz/go,vsekhar/elastic-go,ImJasonH/go,CAFxX/go,codestation/go,linux-on-ibm-z/go,codestation/go,golang/go,Cofyc/go,suncycheng/go,akutz/go,nawawi/go,CAFxX/go,akutz/go,suncycheng/go,golang/go,suncycheng/go,linux-on-ibm-z/go,derekmarcotte/go,cloudflare/go,akutz/go,christopher-henderson/Go,golang/go,CAFxX/go,nawawi/go,linux-on-ibm-z/go,vsekhar/elastic-go,akutz/go,suncycheng/go,nawawi/go,codestation/go,josharian/go,polyverse-security/go,Cofyc/go,nawawi/go,derekmarcotte/go,CAFxX/go,ImJasonH/go,Cofyc/go,josharian/go,golang/go,akutz/go,codestation/go,linux-on-ibm-z/go,nawawi/go,golang/go,CAFxX/go,derekmarcotte/go,ImJasonH/go,derekmarcotte/go,ImJasonH/go,linux-on-ibm-z/go,derekmarcotte/go,vsekhar/elastic-go,derekmarcotte/go,ImJasonH/go,vsekhar/elastic-go,CAFxX/go,josharian/go,codestation/go,codestation/go,polyverse-security/go,polyverse-security/go,cloudflare/go,suncycheng/go,akutz/go,josharian/go,CAFxX/go,suncycheng/go,codestation/go,Cofyc/go,derekmarcotte/go