Revert "Rewrite Qt4 based nested yield mutex locking."

This reverts the unx/kde4/KDEXLib.cxx part of

commit 13a34f4c6307d1bd2443cbf3fbd83bfdd8cdbafb.

Conflicts:

	vcl/unx/kde4/KDE4FilePicker.cxx
	vcl/unx/kde4/KDEXLib.cxx

(cherry picked from commit daf011870efae282244c0298494820d9a0c6d3bc)

Change-Id: I4075fc26d54e5abb2e1cdb535d84f16c8fd3df09
Reviewed-on: https://gerrit.libreoffice.org/8705
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>