AutoVM filter updates

Do not remove VM scheduling unit if already present

BUG=None
TEST=UT

Change-Id: Iac71e34e59dfed55593a0e8a34805aab9c1ef148
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/5860131
Tested-by: Varun Srivastav <varunsrivastav@google.com>
Auto-Submit: Varun Srivastav <varunsrivastav@google.com>
Reviewed-by: Derek Beckett <dbeckett@chromium.org>
Commit-Queue: Varun Srivastav <varunsrivastav@google.com>