keybindings: Plug a GSettings instance leak
meta-cursor-tracker: Initialize our position from MetaWaylandPointer's

Clutter's input device initial position defaults to (-1, -1) on most
backends but for the evdev backend we changed it to be inside the
stage to prevent the pointer from wandering outside the stage until it
first enters, after which our constraining callback won't let it go
out.

This makes us be in sync with the real position from the start.
wayland-keyboard: Remove unused modifier indexes

This was copied from weston where they're used for compositor
keybindings. Mutter has its own keybindings code which doesn't need
this.

https://bugzilla.gnome.org/show_bug.cgi?id=722847