Clean up ImsFeature status callbacks correctly in FeatureConnection

1) ImsFeatureStatusCallbacks were not being deregistered when the
MmTelFeatureConnection was removed, causing callbacks to still call
into that FeatureConnection. This caused a memory leak as well as
duplicate callbacks into ImsManager.

2) Small refactor to better decouple the abstract FeatureConnection
from the MmTelFeatureConnection

Bug: 156893040
Fixes: 157948894
Test: atest FrameworksTelephonyTests CtsTelephonyTestCases:ImsServiceTest
Merged-In: Iedf820f9da10088c845b34c2a08658d7204241b3
Change-Id: Iedf820f9da10088c845b34c2a08658d7204241b3
3 files changed
tree: 766431c6b1d709a827909a7d111259b0ee10a5f4
  1. Android.bp
  2. CleanSpec.mk
  3. OWNERS
  4. README.txt
  5. TEST_MAPPING
  6. src/
  7. tests/