The mode is never set after the removal of the bottom tray, so it
no longer makes sense to pass it to allowKeybinding(). We can also
safely remove it from the ActionModes flags altogether without
requiring a synchronized update with gnome-settings-daemon, as
the latter never used any flag value above LOGIN_SCREEN.
When it comes to keybindings or gestures, there's not really a good
reason why popups associated with the top bar should behave differently
from any other shell menus. Just set the action mode generically for
all menus, so actions like screenshots or media-keys start working
with menus like the background- or app launcher context menus.
https://bugzilla.gnome.org/show_bug.cgi?id=745039