Remove |skip_for_pause_| and |skip_for_backgrounded_| for GpuWatchdog

These flags are originally added to fix a problem that WatchdogPause
didn't pause the watchdog in time. (The command has to propograte
from the GpuMain thread to the watchdog thread.) The later fix with
InProgressing() seems enough to handle this issue. Thus the flags
are now removed.

Another purpose to remove these flags is to fix the Android GPU hang
on ~GpuWatchdogThread() when getting the lock for |skip_for_pause_|.

Bug: 382067635
Change-Id: I2286df0eb768b9d690985634fc4bccebb2aed572
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6075781
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Maggie Chen <magchen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1393101}