go/types: remove unused field parameter
go/types: remove unused field parameter

Found by github.com/mvdan/unparam.

Change-Id: Ie26e963176eb7afb35d16fed5cbca6530f7731c3
Reviewed-on: https://go-review.googlesource.com/37832
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
Run-TryBot: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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