Fix ECBM during test mode

An upstream removed duplicate ECBM exit indications from being
generated during ECBM exit. This broke the test procedure using
ril.test.emergencynumber because the modem never sends an exit
inidication in this case.

Bug: 155926465
Test: manual; trigger test emergency call + ECBM
Change-Id: Ia78a839c5b4a66b605ae25041fd74738ff2ab06b