Revert "MDL-35131 Caching: Purge all will clear course modinfo cache …

…- Thanks to Thomas for patch"

This reverts commit 6ab62db.

This is breaking upgrades from 22 - purgeallcaches gets called during upgrade but
rebuild_course_caches is not a safe api to use in this case.

lib/moodlelib.php

@@ -1551,9 +1551,6 @@ function purge_all_caches() {
 
     cache_helper::purge_all();
 
-    // Clear course cache for all courses.
-    rebuild_course_cache(0, true);
-
     // purge all other caches: rss, simplepie, etc.
     remove_dir($CFG->cachedir.'', true);