Floss: Fix headset keeps ringing after accepting call from application

The application should be able to accept the incoming call and stop the
ringing process.
Remove the check of existing HID call in the call list as it can be the
incoming call and it prevents to accept it. Moreover dialing_call() and
answer_call() are already checking the call list.

Bug: 326654037
Test: Conduct the following manual tests
  pair Bluetooth Headset
  login to "Dialpad" via https://dialpad.com/login
  add Headset to "Dialpad" call control by following step:
    Profile -> Preferences -> Hardware Settings -> Call controls
    -> Add Headset -> Select headset and click connect.
  call to "Dialpad" with phone
  check there is a incoming call
  answer call in "Dialpad"
  no ringtone is heard in headset
Test: Conduct the following manual tests
  pair Bluetooth Headset
  load https://google.github.io/libhidtelephony/ with Chrome
  click on "Start", select the headset then "Connect"
  "Inputs Reports" and "Output Reports" are correct
  click on "Ring(1)"
  ringtone is heard in headset
  click on "Off-Hook(1)"
  click on "Ring(0)"
  no ringtone is heard in headset
  click on "Off-Hook(0)"
Test: atest bluetooth_test_gd
Tag: #floss
Flag: EXEMPT, no behavior change on Android; Floss-only changes

Change-Id: Id4af9590c85ce7115d681d182b0d61dc7d3510b9