Temporarily disable App-Bound encryption metrics.

The crypto and data format are changing, so while these CLs land,
disable the metrics, otherwise old metrics data encrypted with the
old code won't decrypt with the new code and failures will spike.

A future CL similar to https://crrev.com/c/5322044 will re-seed
the metrics, once all the CLs have landed.

BUG=41493095

Change-Id: I4071aaa0fe766cfb7fe28f27eeed9a79869ec4de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5388866


Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1277104}