Remove configure probes for sys/ipc.h, sys/sem.h, sys/shm.h.

These are in SUSv2 and every targeted Unix system has them.  It's not
hard to avoid including them on Windows system because they're mostly
used in platform-specific translation units.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA%2BhUKG%2BL_3brvh%3D8e0BW_VfX9h7MtwgN%3DnFHP5o7X2oZucY9dg%40mail.gmail.com

src/backend/port/sysv_sema.c

@@ -17,13 +17,9 @@
 #include <signal.h>
 #include <unistd.h>
 #include <sys/file.h>
-#include <sys/stat.h>
-#ifdef HAVE_SYS_IPC_H
 #include <sys/ipc.h>
-#endif
-#ifdef HAVE_SYS_SEM_H
 #include <sys/sem.h>
-#endif
+#include <sys/stat.h>
 
 #include "miscadmin.h"
 #include "storage/ipc.h"

src/backend/port/sysv_shmem.c

@@ -22,14 +22,10 @@
 #include <signal.h>
 #include <unistd.h>
 #include <sys/file.h>
-#include <sys/mman.h>
-#include <sys/stat.h>
-#ifdef HAVE_SYS_IPC_H
 #include <sys/ipc.h>
-#endif
-#ifdef HAVE_SYS_SHM_H
+#include <sys/mman.h>
 #include <sys/shm.h>
-#endif
+#include <sys/stat.h>
 
 #include "miscadmin.h"
 #include "port/pg_bitutils.h"

src/backend/storage/ipc/dsm_impl.c

@@ -53,13 +53,9 @@
 #include <unistd.h>
 #ifndef WIN32
 #include <sys/mman.h>
-#endif
-#include <sys/stat.h>
-#ifdef HAVE_SYS_IPC_H
 #include <sys/ipc.h>
-#endif
-#ifdef HAVE_SYS_SHM_H
 #include <sys/shm.h>
+#include <sys/stat.h>
 #endif
 
 #include "common/file_perm.h"