Revert "HdyHeaderGroup: Disconnect from header bar's signals during dispose"
Since commit c5bf27d4 header bars are
destroyed before header group, so when destroying the header group, the
list of header bars is always empty, so there's nothing to unref anymore.
Reverts commit 14e5fc7b.
5 minutes and 35 seconds
(queued for 1 minute and 16 seconds)