Cleanup and removed BTIF-related unused code

* Removed field tBTIF_MEDIA_CB.av_sm_hdl, because it is never used
  after an assignment.
* Removed the corresponding function btif_av_get_sm_handle() which
  is not used/needed anymore.
* Declared btif_hf_is_call_idle() function in a new header file
  "btif_hf.h"
* Removed tBTIF_STATUS, BTIF_SUCCESS and BTIF_ERROR_SRV_* error codes
  which are never used.
* Removed duplicate conditional define of BTA_AV_CO_CP_SCMS_T
* Removed unused typedef tBTA_AV_AUDIO_CODEC_INFO, and unused
  BTA_AV_CO_* defines and enums.

Change-Id: I7bb49957fad94073d474fea6ea0d466f36df37fb