tests: remove unnecessary lines from queue-test

Earlier, the wl_display_dispatch_pending were setting number of thread
that can dispatch events. This behaviour was removed later,
so now these lines are redundant.

Related commits:

385fe30e
78cfa967
3c7e8bfb

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>