Remove mate-tweak helper, old patch now in upstream src

The flidas make-mate-tweak helper was adding a single line...

--unredir-if-possible-exclude "class_g = 'Mate-screensaver'" \

.. to the marco-compton and metacity-compton scripts. The marco-compton line is now included in the upstream code for mate-tweak in bionic, and the metacity-compton script no longer exists.

https://github.com/ubuntu-mate/mate-tweak/blob/8dd9931aa57ed176fef01cf516c8f4cf90cf9d4e/marco-compton#L42

I have installed upstream mate-tweak_18.04.16-1_all.deb and it seems to be working.