The raw_data member is used for passing heap allocated data with an event,
(e.g. strings of dtmf data) the memory is freed after the event has been processed.

Recent changes in the event structure added a way to pass sig status changes inline,
so remove the raw_data usage for FTDM_SIGEVENT_SIGSTATUS_CHANGED events.

NOTE: This (finally) fixes a bug in ftmod_libpri that was caused by
      the event handling changes (stack corruption due to using free()
      on a variable on the stack, which turned into a NULL ptr deref
      caused by some compat code in ftdm_io.c:ftdm_span_send_signal().

Compiles and tested on my BRI setup, i did a quick audit of all
places that generate FTDM_SIGEVENT_SIGSTATUS_CHANGED events and
except for the sangoma_boost module there's nothing else that left
using raw_data for this event.
Signed-off-by: Stefan Knoblich <s.knoblich@axsentis.de>