Remove QAction menu icons on Mac.

In general Mac apps do not have menu icons, except for a few rare
cases (and generally just black-and-white).

Change-Id: I5b1501d723ae5ae9e495878bf741a1d755c42a45
Merge topic 'FIX_remove_menu_icons_on_mac' into master

2646815e Remove QAction menu icons on Mac.