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/utils/cache/catcache.c

@@ -39,7 +39,6 @@
 #include "utils/rel.h"
 #include "utils/resowner_private.h"
 #include "utils/syscache.h"
-#include "utils/tqual.h"
 
 
  /* #define CACHEDEBUG */	/* turns DEBUG elogs on */

src/backend/utils/cache/relcache.c

@@ -90,7 +90,6 @@
 #include "utils/resowner_private.h"
 #include "utils/snapmgr.h"
 #include "utils/syscache.h"
-#include "utils/tqual.h"
 
 
 #define RELCACHE_INIT_FILEMAGIC		0x573266	/* version ID value */

src/backend/utils/cache/ts_cache.c

@@ -47,7 +47,6 @@
 #include "utils/memutils.h"
 #include "utils/regproc.h"
 #include "utils/syscache.h"
-#include "utils/tqual.h"
 
 
 /*