xdg: Eliminate redundant update_x/update_y flags

xdg: Eliminate redundant update_x/update_y flags

struct view's pending_move_resize.update_x/update_y flags appear to
be redundant, since we can easily determine whether x/y have been
update via a simple comparison in handle_commit().

The only corner case I can think of where this change might affect
behavior, is if xdg_toplevel_view_move() is called while a resize
is still pending (e.g. after xdg_toplevel_view_configure() but
before handle_commit()). This corner case will be addressed in the
following commit.