commentText is only called if g != nil in ParseGo, so the check inside
commentText is redundant and can be deleted.

Change-Id: I130c18b738527c96bc59950b354a50b9e23f92e9
Reviewed-on: https://go-review.googlesource.com/74871
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>