Remove unnecessary #include.

Discussion: https://postgr.es/m/4380.1547143967@sss.pgh.pa.us

Author: tglsfdc

src/include/optimizer/appendinfo.h

@@ -14,7 +14,6 @@
 #ifndef APPENDINFO_H
 #define APPENDINFO_H
 
-#include "nodes/plannodes.h"
 #include "nodes/relation.h"
 #include "utils/relcache.h"