Further fixes on VIMS.onPreCreatedUserConversion()

Previously, when onRoleHoldersChanged() was called in a pre-created
user, VoiceInteractionManagerService (A.K.A. VIMS) would store that
user id and call the method again when the pre-converted user is
converted to a real user (on onPreCreatedUserConversion()), as the
assistant role holders is not available for pre-created users.

But if the system restarts between the user pre-creation and
conversion, onPreCreatedUserConversion() would log a warning and
do nothing.

So, this CL gets rids of the "save the user id" part, and simply
re-call onRoleHoldersChanged() whenever a pre-created user is
converted.

Test: manual verification on automotive builds
Bug: 242254421

Change-Id: Id933b2bc4f887da8b2f4959955bd174ed5879a47