build: drop check for udev_monitor_set_receive_buffer_size

It has been exported by systemd commit
commit a571c23e954cb88cdd5faa28593b19bd7c340130
    libudev: export udev_monitor_set_receive_buffer_size()
released in v183.
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>

m4/virt-udev.m4

@@ -28,16 +28,6 @@ AC_DEFUN([LIBVIRT_CHECK_UDEV],[
   if test "$with_udev" = "yes" && test "$with_pciaccess" != "yes" ; then
     AC_MSG_ERROR([You must install the pciaccess module to build with udev])
   fi
-
-  if test "$with_udev" = "yes" ; then
-    old_CFLAGS="$CFLAGS"
-    old_LIBS="$LIBS"
-    CFLAGS="$CFLAGS $UDEV_CFLAGS"
-    LIBS="$CFLAGS $UDEV_LIBS"
-    AC_CHECK_FUNCS([udev_monitor_set_receive_buffer_size])
-    CFLAGS="$old_CFLAGS"
-    LIBS="$old_LIBS"
-  fi
 ])
 
 AC_DEFUN([LIBVIRT_RESULT_UDEV],[

src/node_device/node_device_udev.c

@@ -1847,14 +1847,12 @@ nodeStateInitialize(bool privileged,
 
     udev_monitor_enable_receiving(priv->udev_monitor);
 
-#if HAVE_UDEV_MONITOR_SET_RECEIVE_BUFFER_SIZE
     /* mimic udevd's behaviour and override the systems rmem_max limit in case
      * there's a significant number of device 'add' events
      */
     if (geteuid() == 0)
         udev_monitor_set_receive_buffer_size(priv->udev_monitor,
                                              128 * 1024 * 1024);
-#endif
 
     if (virThreadCreate(&priv->th, true, udevEventHandleThread, NULL) < 0) {
         virReportSystemError(errno, "%s",