go/token: remove excess parenthesis in NoPos.IsValid() documentation
go/token: remove excess parenthesis in NoPos.IsValid() documentation

Fixes #20294

Change-Id: I32ac862fe00180210a04103cc94c4d9fef5d1b6c
Reviewed-on: https://go-review.googlesource.com/42992
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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