runtime: fix out of date comments
runtime: fix out of date comments

The transition from mark 1 to mark 2 no longer enqueues new root
marking jobs, but some of the comments still refer to this. Fix these
comments.

Change-Id: I3f98628dba32c5afe30495ab495da42b32291e9e
Reviewed-on: https://go-review.googlesource.com/24965
Reviewed-by: Rick Hudson <838bd060584c511f21c75c69ea04b7b120d86af0@golang.org>

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