fix Telecom out of sync w/ Telephony#defaultVoiceSubId

Sony reported an edge case bug in call preferences.

When all sims were removed, Telephony sends the signal
to both:

(1) set the defaultVoiceSubId=-1 (INVALID_SUB_ID)
(2) set the default phoneAccountHandle=null

The getUserDefaultPhoneAccountHandle would temporarily
return null and never actually change the value in Telecom
because it was gated by a conditional check. However, upon
re-inserting the sims, the call preference from before would
be restored (before setting the value to null).

This would cause Telephony and Telecom to become out of sync.
Telephony showed voiceSubId=-1 while Telecom showed the default
phoneAccountHandle != null

Therefore, no longer want to rely on getUserDefaultPhoneAccountHandle
to change the default phoneAccountHandle from the Telephony side
of things.

bug: 204226202
Test: manual
Change-Id: I56b0eaaaa7a0eb998c0feb0859983dd6c5ddfc1b