Fix obsolete references to postgres.h in comments.

Oversights in commits d08741eab5 and d952373a98.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/aMxbfSJ2wLWd32x-%40nathan

src/include/access/htup_details.h

@@ -634,7 +634,7 @@ BITMAPLEN(int NATTS)
  * MaxAttrSize is a somewhat arbitrary upper limit on the declared size of
  * data fields of char(n) and similar types.  It need not have anything
  * directly to do with the *actual* upper limit of varlena values, which
- * is currently 1Gb (see TOAST structures in postgres.h).  I've set it
+ * is currently 1Gb (see TOAST structures in varatt.h).  I've set it
  * at 10Mb which seems like a reasonable number --- tgl 8/6/00.
  */
 #define MaxAttrSize		(10 * 1024 * 1024)

src/include/c.h

@@ -659,7 +659,7 @@ typedef uint32 CommandId;
  * representation is no longer convenient.  It's recommended that code always
  * use macros VARDATA_ANY, VARSIZE_ANY, VARSIZE_ANY_EXHDR, VARDATA, VARSIZE,
  * and SET_VARSIZE instead of relying on direct mentions of the struct fields.
- * See postgres.h for details of the TOASTed form.
+ * See varatt.h for details of the TOASTed form.
  * ----------------
  */
 struct varlena

src/include/utils/expandeddatum.h

@@ -95,7 +95,7 @@ typedef struct ExpandedObjectMethods
  * But note that these pointers are just a convenience; a pointer object
  * appearing somewhere else would still be legal.
  *
- * The typedef declaration for this appears in postgres.h.
+ * The typedef declaration for this appears in varatt.h.
  */
 struct ExpandedObjectHeader
 {

src/include/utils/memutils.h

@@ -30,7 +30,7 @@
  *
  * palloc() enforces MaxAllocSize, chosen to correspond to the limiting size
  * of varlena objects under TOAST.  See VARSIZE_4B() and related macros in
- * postgres.h.  Many datatypes assume that any allocatable size can be
+ * varatt.h.  Many datatypes assume that any allocatable size can be
  * represented in a varlena header.  This limit also permits a caller to use
  * an "int" variable for an index into or length of an allocation.  Callers
  * careful to avoid these hazards can access the higher limit with

src/include/utils/varbit.h

@@ -20,7 +20,7 @@
 #include "fmgr.h"
 
 /*
- * Modeled on struct varlena from postgres.h, but data type is bits8.
+ * Modeled on struct varlena from c.h, but data type is bits8.
  *
  * Caution: if bit_len is not a multiple of BITS_PER_BYTE, the low-order
  * bits of the last byte of bit_dat[] are unused and MUST be zeroes.