MDL-50049 deprecation: Extra minor fixes.

- complete and cleanup upgrade.txt
- replace remaining uses in comments.
- fix some incorrect bulk-replacement in previous commit.

lib/setuplib.php

@@ -328,7 +328,7 @@ class file_serving_exception extends moodle_exception {
 }
 
 /**
- * Default exception handler, uncaught exceptions are equivalent to error() in 1.9 and earlier
+ * Default exception handler.
  *
  * @param Exception $ex
  * @return void -does not return. Terminates execution!