obs-outputs: Remove unused macro

plugins/obs-outputs/flv-mux.c

@@ -29,7 +29,6 @@
 //#define DEBUG_TIMESTAMPS
 //#define WRITE_FLV_HEADER
 
-#define VIDEO_HEADER_SIZE 5
 #define VIDEODATA_AVCVIDEOPACKET 7.0
 #define AUDIODATA_AAC 10.0