workspace: Remove no longer valid comment

This comment is no longer correct, we're not inserting any actors here
to adjust for the window border, but we're modifying the allocation of
the children to adjust for that border.

Since that happens in the layout manager anyway, remove the comment
here.

GNOME/gnome-shell!1297
9 jobs for !1297 with window-clones-new-layout in 8 minutes and 16 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Review
passed #751265
check_commit_log

00:00:48

passed #751267
eslint

00:02:27

passed #751266
js_check

00:01:30

passed #751269
no_template_check

00:01:38

passed #751268
potfile_check

00:00:54

 
  Build
passed #751270
build

00:03:51

passed #751271
flatpak
flatpak

00:03:21

 
  Test
passed #751272
test

00:01:55

passed #751273
test-pot

00:00:50