Revert "[voicecall] Disabled usage of tpring for calls."

This reverts commit e8edba9e7142d3dcfa2cb0b21e7071734ddf9156.
Revert "[voicecall] More removing telepathy-ring specific call handling."

This reverts commit a1db4d9a78edd91424810a18ea127d087adbfe82.