wayland: make deliver_key_event return void

wayland: make deliver_key_event return void

deliver_key_event is sometimes called from a timeout handler and
sometimes called directly.  We currently erroneously return TRUE
(G_SOURCE_CONTINUE) in the case where it's called directly, but to
no ill effect, since we ignore that return value. In the future,
we're going to need to call it directly in other parts of the code
where the return value would be relevant and handling TRUE, would
require adding redundant code.

Instead, this commit just changes the code to always reset the timer
manually, and never rely on glib's ability to automatically reset
the timer by returning TRUE.  This makes the code smaller, too, since
there's less special casing required.

https://bugzilla.gnome.org/show_bug.cgi?id=757942