Clean up start() parameters

Document where int is used instead of AudioSystem::sync_event_t
  (probably because of a header file dependency).
TrackBase::start() and RecordTrack::start() don't need default parameters.

Change-Id: I82f4a4d078be900f3aa4bd926697e32f5ed68ec8
diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index 4c0ad7c..fe9d09d 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -5867,7 +5867,7 @@
     return mRecordTrack->getCblk();
 }
 
-status_t AudioFlinger::RecordHandle::start(int event, int triggerSession) {
+status_t AudioFlinger::RecordHandle::start(int /*AudioSystem::sync_event_t*/ event, int triggerSession) {
     ALOGV("RecordHandle::start()");
     return mRecordTrack->start((AudioSystem::sync_event_t)event, triggerSession);
 }