shell: Don't force basic render loop for Plasma Mobile

The basic render loop seems to cause the panels to not visually appear, with some Wayland error: teams/plasma-mobile/issues#182 (closed) I have no clue why, if there is a better fix it would be better for that to replace this...

This is quite urgent and needs to be cherry picked to 5.26, or else 5.26.4 will result in Plasma Mobile having no panels.