Minor clean up of css/js

* Trim trailing whitespace on lines.
* Remove css that has been commented for 5 years (63e25672).
* Remove comment about $wgCategoryTreeVersion which was
  removed 2 years ago (e77ae54).
* Add missing spaces in CSS and JS.

Change-Id: Icb28293b445880246f2b4273daab2fb21c2638df