Instead of handling the URCs in the modem object and using the
MMIfaceModem as a bridge to report the status read from the URC to a
call obtained from the MMCallList... just handle the URCs in the call
object itself.
Call information only lives in the ModemManager logic, there is no
associated date stored within the device itself. Therefore, simplify
everything by assuming there is nothing to remove.
Looks like this logic was implemented because it was originally based
on the SMS management logic, but for SMS we do have to remove
them (the stored PDU parts) from the device.
Commit a08064492 ("call-list: port mm_call_list_delete_call to use GTask")
ported most of the mm_call_list_delete_call code to use GTask, but missed a
g_simple_async_report_error_in_idle calls, which can potentially lead to
an incorrect G_TASK cast in mm_call_list_delete_call_finish.
When calling g_list_free_full() to free a GList in dispose(), it is
necessary to reset the GList pointer to NULL as dispose() may be called
more than once.
g_free and g_object_unref are in form of `void (*)(gpointer)`, which
matches the GDestroyNotify signature. An explicit GDestroyNotify cast on
g_free and g_object_unref is thus not needed.
