Correct REMOVE_USER change mode.

REMOVE_USER change mode should not be static. Correct it in our
doc to on_change. Updates VTS to allow both for backward
compatibility.

Test: Presubmit
Flag: EXEMPT doc VTS
Bug: 401350376
Change-Id: Ib0420d67aba97be18c564b4a3cc25402435068c6
5 files changed