test: remove timer in test-dgram-send-empty-array

The timer is not necessary. The test will timeout via the test harness
if the test fails. This should resolve spurious CI failures.

PR-URL: https://github.com/nodejs/node/pull/9361


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>