Remove fmgr.h includes from headers that don't really need it.

Most of the fmgr.h includes were obsoleted by 352a24a1f9. A
few others can be obsoleted using the underlying struct type in an
implementation detail.

Author: Andres Freund
Discussion: https://postgr.es/m/20190803193733.g3l3x3o42uv4qj7l@alap3.anarazel.de

src/include/access/brin.h

@@ -10,7 +10,6 @@
 #ifndef BRIN_H
 #define BRIN_H
 
-#include "fmgr.h"
 #include "nodes/execnodes.h"
 #include "utils/relcache.h"
 

src/include/access/gist_private.h

@@ -17,7 +17,6 @@
 #include "access/amapi.h"
 #include "access/gist.h"
 #include "access/itup.h"
-#include "fmgr.h"
 #include "lib/pairingheap.h"
 #include "storage/bufmgr.h"
 #include "storage/buffile.h"

src/include/access/hash.h

@@ -20,7 +20,6 @@
 #include "access/amapi.h"
 #include "access/itup.h"
 #include "access/sdir.h"
-#include "fmgr.h"
 #include "lib/stringinfo.h"
 #include "storage/bufmgr.h"
 #include "storage/lockdefs.h"

src/include/access/spgist.h

@@ -16,7 +16,6 @@
 
 #include "access/amapi.h"
 #include "access/xlogreader.h"
-#include "fmgr.h"
 #include "lib/stringinfo.h"