fdo#72420 Startcenter: help button point to local/wiki help, ui part

Not handle clicking help button manually but use the default gtk-help
button which will point to the corresponding help files depend
on helpids.

(cherry picked from commit 55fcca64a7d006f8cb10268fd2e1e09b1618a800)

Change-Id: I7ac4b51868d1a5828c810b1ac629d5a56ffb6f50
Reviewed-on: https://gerrit.libreoffice.org/7365
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>