Reset IMS Capabilities when IMS disconnects

When IMS deregisters, reset the IMS capabilities
to false so we do not accidently return the wrong
result for TelephonyManager.isVolteAvailable()
if the ImsService does not set the capabilities to
false before deregistering.

Test: Telephony Unit Tests
Bug: 36374918
Change-Id: I42b066f8a97770f23d71a0c646f384f7cbfdb57b