TeleService: Fix issue can't answer/reject call when at USSD content view

Without appending to the dialog ;)

Change-Id: I4859ba19ee33a05aef940f1d7d8d71e68b591314
Revert "TeleService: Fix issue can't answer/reject call when at USSD content view"

This reverts commit a368bdbbd17d3cf975a85b0973afeeaaef9d264e.

Change-Id: I809b8ce72cfee86da62b3233cac25659dd2d3cd4
TeleService: Null out the dialog when dismissed

Change-Id: I410de20ca21ca6947bef791fb958b4d21b2e4004
Telephony: Use correct string for missed video calls notification

Change-Id: I8cb16e4999147874c7ff1c39a35af01f9b0d82bc