refactor: Use same prototype for neon_read_at_lsn on all PG versions (#11457)

The 'neon_read' function needs to have a different prototype on PG < 16,
because it's part of the smgr interface. But neon_read_at_lsn doesn't
have that restriction.

pgxn/neon/pagestore_client.h

@@ -274,13 +274,8 @@ typedef struct
 	XLogRecPtr effective_request_lsn;
 } neon_request_lsns;
 
-#if PG_MAJORVERSION_NUM < 16
-extern PGDLLEXPORT void neon_read_at_lsn(NRelFileInfo rnode, ForkNumber forkNum, BlockNumber blkno,
-										 neon_request_lsns request_lsns, char *buffer);
-#else
 extern PGDLLEXPORT void neon_read_at_lsn(NRelFileInfo rnode, ForkNumber forkNum, BlockNumber blkno,
 										 neon_request_lsns request_lsns, void *buffer);
-#endif
 extern int64 neon_dbsize(Oid dbNode);
 
 /* utils for neon relsize cache */

pgxn/neon/pagestore_smgr.c

@@ -3154,13 +3154,8 @@ neon_writeback(SMgrRelation reln, ForkNumber forknum,
  * The offsets in request_lsns, buffers, and mask are linked.
  */
 static void
-#if PG_MAJORVERSION_NUM < 16
-neon_read_at_lsnv(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber base_blockno, neon_request_lsns *request_lsns,
-				  char **buffers, BlockNumber nblocks, const bits8 *mask)
-#else
 neon_read_at_lsnv(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber base_blockno, neon_request_lsns *request_lsns,
 				  void **buffers, BlockNumber nblocks, const bits8 *mask)
-#endif
 {
 	NeonResponse *resp;
 	uint64		ring_index;
@@ -3356,13 +3351,8 @@ Retry:
  * To avoid breaking tests in the runtime please keep function signature in sync.
  */
 void
-#if PG_MAJORVERSION_NUM < 16
-neon_read_at_lsn(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
-				 neon_request_lsns request_lsns, char *buffer)
-#else
 neon_read_at_lsn(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
 				 neon_request_lsns request_lsns, void *buffer)
-#endif
 {
 	neon_read_at_lsnv(rinfo, forkNum, blkno, &request_lsns, &buffer, 1, NULL);
 }

pgxn/neon_test_utils/neontest.c

@@ -50,13 +50,8 @@ PG_FUNCTION_INFO_V1(trigger_segfault);
  * Linkage to functions in neon module.
  * The signature here would need to be updated whenever function parameters change in pagestore_smgr.c
  */
-#if PG_MAJORVERSION_NUM < 16
-typedef void (*neon_read_at_lsn_type) (NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
-									   neon_request_lsns request_lsns, char *buffer);
-#else
 typedef void (*neon_read_at_lsn_type) (NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
 									   neon_request_lsns request_lsns, void *buffer);
-#endif
 
 static neon_read_at_lsn_type neon_read_at_lsn_ptr;