wayland: Avoid running stale cursor animation timeouts

wayland: Avoid running stale cursor animation timeouts

gdk_wayland_device_update_window_cursor() is inconsistently returning
TRUE/FALSE, despite the timeout being always replaced for new cursor
frames. This could end up in these timeouts being "leaked" and running
as long as the window has an animated cursor.

Fix this by making it really sure we return G_SOURCE_REMOVE, although
now we keep track of animation delays, so the timeout will be reused
for constant time animations.