runtime: update runtime2.go itab comments about sync struct
runtime: update runtime2.go itab comments about sync struct

`cmd/compile/internal/gc/reflect.go:/^func.dumptypestructs` was modified many times, now is  `cmd/compile/internal/gc/reflect.go:/^func.dumptabs`

Change-Id: Ie949a5bee7878c998591468a04f67a8a70c61da7
GitHub-Last-Rev: 9ecc26985ef18c8e870649b46419db0a9c72054f
GitHub-Pull-Request: golang/go#34489
Reviewed-on: https://go-review.googlesource.com/c/go/+/197037
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

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