cmd/compile/internal/syntax: update a couple of comments
cmd/compile/internal/syntax: update a couple of comments

Change-Id: Ie84d0e61697922c1e808d815fb7d9aec694ee8e9
Reviewed-on: https://go-review.googlesource.com/104615
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>

Cofyc/go,nawawi/go,akutz/go,golang/go,josharian/go,nawawi/go,CAFxX/go,nawawi/go,CAFxX/go,nawawi/go,golang/go,Cofyc/go,cloudflare/go,Cofyc/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,josharian/go,Cofyc/go,akutz/go,akutz/go,josharian/go,CAFxX/go,CAFxX/go,josharian/go,golang/go,CAFxX/go,golang/go,nawawi/go,Cofyc/go,josharian/go,akutz/go,CAFxX/go,Cofyc/go,CAFxX/go,golang/go,cloudflare/go,akutz/go,Cofyc/go,josharian/go,akutz/go,josharian/go,josharian/go,cloudflare/go,cloudflare/go,golang/go,nawawi/go,akutz/go,Cofyc/go,nawawi/go,akutz/go,cloudflare/go,golang/go