Do not set separate challenge flag before clearing lock

Do not set separate challenge flag before clearing lock

This step is redundant since clearLock() would set the flag internally anyway.
In fact setting the flag before calling clearLock() is wrong since it will
lead LockSettingsService.setLockCredential() to think that the target profile
does not have a unified challenge, causing it to use an incorrect existing
credential for password change, leading to untrusted credential change.

Bug: 77892111
Test: Create profile; set separate empty work challenge; observe no crash
Change-Id: I4d76b20706a796654f9389f31ae8c46d51d7adac