Remove superfluous tqual.h includes.

Most of these had been obsoleted by 568d4138c / the SnapshotNow
removal.

This is is preparation for moving most of tqual.[ch] into either
snapmgr.h or heapam.h, which in turn is in preparation for pluggable
table AMs.

Author: Andres Freund
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de

src/backend/access/nbtree/nbtinsert.c

@@ -24,7 +24,6 @@
 #include "storage/lmgr.h"
 #include "storage/predicate.h"
 #include "storage/smgr.h"
-#include "utils/tqual.h"
 
 /* Minimum tree height for application of fastpath optimization */
 #define BTREE_FASTPATH_MIN_LEVEL	2

src/backend/access/nbtree/nbtsearch.c

@@ -22,7 +22,6 @@
 #include "storage/predicate.h"
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
-#include "utils/tqual.h"
 
 
 static bool _bt_readpage(IndexScanDesc scan, ScanDirection dir,