Call onOutgoingEmergencyCall only once.

For backwards compatibility, instead of calling both the old and new
versions of onOutgoingEmergencyCall, only call the new version, and call
the old version from the default impl of the new version instead.

Change suggested by API council.

Bug: 166230518
Test: atest CtsTelecomTestCases:OutgoingCallTest
Change-Id: Ifa9276cc615d0e33d37ebc702dbc0cd155e0d489