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/backends/meta-cursor.c

@@ -111,8 +111,8 @@ translate_meta_cursor (MetaCursor cursor)
 }
 
 Cursor
-meta_cursor_create_x_cursor (Display    *xdisplay,
-                             MetaCursor  cursor)
+meta_create_x_cursor (Display    *xdisplay,
+                      MetaCursor  cursor)
 {
   return XcursorLibraryLoadCursor (xdisplay, translate_meta_cursor (cursor));
 }