Update simple_performant robots.txt and move config setting

* /w/ is used as the script path, not /wiki/
* Based on tests, it does not seem that /skins URLs work (e.g.
  /skins/common/ajax.js corresponds to a path in core, but is a 404)
* Move simple_performant cache setting to role

Change-Id: I936a88009ee2d296bbd777b62fca8524e4f48c0e
Merge "Update simple_performant robots.txt and move config setting"