Cleanup: remove redundant headers in source/blender/editors/

Remove redundant headers using
`./source/tools/utils_maintenance/code_clean.py`

Reviewed By: jmonteath

Ref D10364

source/blender/editors/space_sequencer/sequencer_edit.c

@@ -28,7 +28,6 @@
 #include "MEM_guardedalloc.h"
 
 #include "BLI_blenlib.h"
-#include "BLI_ghash.h"
 #include "BLI_math.h"
 #include "BLI_timecode.h"
 #include "BLI_utildefines.h"