Quota: remove code for quotachange event/Storage Pressure API.

The flag was not enabled, so there should be no behavioral change.

Bug: 4027659
Change-Id: I1a323a45d97b661a574f046a61954397439d48a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5930607
Commit-Queue: Evan Stade <estade@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1370046}