Revert "Implement zoom"

[lenemter]

Reverts #739
Fixes #740

[ryonakano]

This is an issue with debian packaging. We added the new io.elementary.greeter-compositor.gschema.xml file in the #739 but it's not included in the deb file, which results the null access here:

        var schema = new GLib.Settings ("io.elementary.greeter-compositor.keybindings");

        display.add_keybinding ("zoom-in", schema, Meta.KeyBindingFlags.NONE, (Meta.KeyHandlerFunc) zoom_in);
        display.add_keybinding ("zoom-out", schema, Meta.KeyBindingFlags.NONE, (Meta.KeyHandlerFunc) zoom_out);

[ryonakano]

Closing because the linked issue should be fixed by 89dff87, but thank you for your quick response anyways, @lenemter!