Handle Dead Objects from Phone Crashes better

1) Check to make sure ImsService is available when calling
changeMmTelCapability.
2) Remove caching of ImsConfig in ImsManager. It is already
cached properly in MmTelFeatureConnection.
3) Create a DeathRecipient for MmTelFeature in
MmTelFeatureConnection that cleans up all caches and notifies
ImsManager that the connection is now unavailable.

Bug: 77941698
Test: Manual
Change-Id: I9c3721fe275a94f7f8841e8e84a2f9d8a3c4823b