Remove null checks for undead widgets in MouseLockDispatcher code

RenderWidget is never entered by IPC when undead or provisional, not
by C++ outside of Close() when undead. Branches can go away.

R=avi@chromium.org

Bug: 419087
Change-Id: Iebcd2501b60d3836d66acd6d64787d41322e8641
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1854522
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704947}
1 file changed