This reverts commit https://golang.org/cl/161177/.

Reason for revert: this led to non-contiguous comments spaced
by an empty line to be grouped into a single CommentGroup

Fixes #32944
Updates #10858

Change-Id: I5e16663b308c3b560496da8e66c33befdf9ed9dd
Reviewed-on: https://go-review.googlesource.com/c/go/+/185040Reviewed-by: Robert Griesemer <gri@golang.org>