Remove an unused (and empty) header file.

src/include/lib/lispsort.h

-/*-------------------------------------------------------------------------
- *
- * lispsort.h
- *
- *
- *
- * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * $PostgreSQL: pgsql/src/include/lib/lispsort.h,v 1.13 2003/11/29 22:41:02 pgsql Exp $
- *
- *-------------------------------------------------------------------------
- */
-#ifndef LISPSORT_H
-#define LISPSORT_H
-
-#endif   /* LISPSORT_H */