Bluetooth: Remove strings for enabling inband ringing

* As in-band ringing is enabled by default on supported devices, user
  action in development settings should be disabling it instead of
  enabling it
* The new string is added to packages/apps/Settings and the old string
  is hence removed from SettingsLib

Bug: 65383086
Test: make, try toggling the preference and verify in-band ringing's
      behavior
Change-Id: I18858e86f4127f6555cce27d239d2682b6134fe2