[remoting host] Simplify capture scheduling logic

This removes an unnecessary section from
WebrtcFrameSchedulerSimple::ScheduleNextFrame()
to address review comments on
https://chromium-review.googlesource.com/940449
and potentially improves performance and b/w utilization.

Bug: 816727
Change-Id: I76aaf326a48f985880ea7ff4ba4e16cc246862b3
Reviewed-on: https://chromium-review.googlesource.com/942484


Reviewed-by: Zijie He <zijiehe@chromium.org>
Commit-Queue: Lambros Lambrou <lambroslambrou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540276}