ambient: remove kReleaseWakeLockDelay

|kReleaseWakeLockDelay| is an experimental value we found denoting the
time from releaseing the wake lock to the display actually being turned
off. The delay is defined by the inactivity timer per crbug.com/190499.
For screen saver duration, since all the options are at least 5 minutes,
the duration should be insensitive to an extra 38 seconds delay. Remove
the delay for code simplicity.

BUG=b:278939395
TEST=ash_unittests --gtest_filter="*AmbientController*"

Change-Id: I77ddba080e286a44fa46dafdbf0730018db7871d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4824707
Reviewed-by: Tao Wu <wutao@chromium.org>
Commit-Queue: Jerry Liu <pzliu@google.com>
Cr-Commit-Position: refs/heads/main@{#1189973}