backends/cursor: Rename X11 cursor creation function

It was prefixed with meta_cursor_, but it took a X11 Display, so update
the naming. Eventually it should be duplicated depending if it's a
frontend X11 connection call or a backend X11 connection call and moved
to the corresponding layers, but let's just do this minor cleanup for
now.

https://gitlab.gnome.org/GNOME/mutter/issues/77

src/core/display.c

@@ -3018,7 +3018,7 @@ Cursor
 meta_display_create_x_cursor (MetaDisplay *display,
                               MetaCursor   cursor)
 {
-  return meta_cursor_create_x_cursor (display->xdisplay, cursor);
+  return meta_create_x_cursor (display->xdisplay, cursor);
 }
 
 MetaGestureTracker *