appDisplay: Disconnect from parental controls on destroy

BaseAppView not disconnecting from the 'app-filter-changed'
signal means parental controls may trigger callbacks on
a destroyed grid, which tries to access destroyed icons,
which spams the journal with stack traces.

Disconnect from parental controls when BaseAppView is destroyed.

GNOME/gnome-shell!1441
parent ff9001d0
Pipeline #214480 passed with stages
in 4 minutes and 15 seconds