Replace heapam.h includes with {table, relation}.h where applicable.

A lot of files only included heapam.h for relation_open, heap_open etc
- replace the heapam.h include in those files with the narrower
header.

Author: Andres Freund
Discussion: https://postgr.es/m/20190111000539.xbv7s6w7ilcvm7dp@alap3.anarazel.de

contrib/pageinspect/btreefuncs.c

@@ -30,7 +30,7 @@
 #include "pageinspect.h"
 
 #include "access/nbtree.h"
-#include "access/heapam.h"
+#include "access/relation.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_am.h"
 #include "funcapi.h"

contrib/pageinspect/heapfuncs.c

@@ -27,8 +27,8 @@
 
 #include "pageinspect.h"
 
-#include "access/heapam.h"
 #include "access/htup_details.h"
+#include "access/relation.h"
 #include "funcapi.h"
 #include "catalog/pg_type.h"
 #include "miscadmin.h"

contrib/pageinspect/rawpage.c

@@ -18,7 +18,7 @@
 #include "pageinspect.h"
 
 #include "access/htup_details.h"
-#include "access/heapam.h"
+#include "access/relation.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"