Don't delete corp policy key when running updater tests.

The issue here is that running non-elevated tests can't
delete the corp policy keys, so the tests fail when run
on a developer system, which happens to have any corp
policies set.

The CL removes the deletion of the corp policy key.
Instead of that, it attempts the cleanup of the
updater's device management key, which the updater creates.

If the tests fail on the dev system, then these device
management keys must be cleaned up manually for the tests
to pass.

Bug: 1206858
Change-Id: I86b7ad01a71da1bcaee79beaab786e1f1ceebcfd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2881184


Reviewed-by: S. Ganesh <ganesh@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#880648}