Floss: Remove automatic SCO call start

The telephony functions were implemented only for qualification and they
don't care about CRAS at all. But now they should release the SCO
management back to CRAS.

Bug: 299231669
Test: Conduct the following manual tests.
  pair Bluetooth Headset
  load https://google.git.io/libhidtelephoony/ with Chrome
  click on "Start", select the headset then "Connect"
  "Inputs Reports" and "Output Reports" are correct
  "Hook Switch" and "Ring" test cases are passed
Test: atest bluetooth_test_gd

Change-Id: I43efc81e4437fec203a07935eab868922627d08a