Merge "Revert "Move IMS to a listener type model instead of a poll model"" am: 0ad2adeb48 am: ff98cd706b

Original change: https://android-review.googlesource.com/c/platform/packages/services/Telephony/+/1443077

Change-Id: I34789daf9b6e2efaf398f0c38ed5c2cb5c6ee658