refine code, remove unused code of dvr.

@@ -48,7 +48,6 @@ SrsFlvSegment::SrsFlvSegment()
     has_keyframe = false;
     duration = 0;
     starttime = -1;
-    sequence_header_offset = 0;
     stream_starttime = 0;
     stream_previous_pkt_time = -1;
     stream_duration = 0;
@@ -63,7 +62,6 @@ void SrsFlvSegment::reset()
     has_keyframe = false;
     starttime = -1;
     duration = 0;
-    sequence_header_offset = 0;
 }
 
 SrsDvrPlan::SrsDvrPlan()

@@ -60,10 +60,6 @@ public:
     */
     bool has_keyframe;
     /**
-    * sequence header offset in file.
-    */
-    int64_t sequence_header_offset;
-    /**
     * current segment starttime, RTMP pkt time.
     */
     int64_t starttime;