Split Python OBJ importer and exporter, enabling only the importer.

This is from patch D13988. It removes the "- New" from the menu of the
new obj exporter, changes the default addon to just io_import_obj,
and does the right versioning thing.
Also disables the python tests for the old python exporter.

source/blender/blenloader/intern/versioning_userdef.c

@@ -973,6 +973,13 @@ void blo_do_versions_userdef(UserDef *userdef)
    */
   {
     /* Keep this block, even when empty. */
+    if (!USER_VERSION_ATLEAST(301, 7)) {
+      /* io_scene_obj directory is gone, split into io_import_obj and io_export_obj,
+       * with io_import_obj enabled by default and io_export_obj replaced by the C++ version.
+       */
+      BKE_addon_remove_safe(&userdef->addons, "io_scene_obj");
+      BKE_addon_ensure(&userdef->addons, "io_import_obj");
+    }
   }
 
   LISTBASE_FOREACH (bTheme *, btheme, &userdef->themes) {