mediawiki.action.history.diff: Rework print styles

* Remove extremely old print styles for diffs from commonPrint.css,
  added back in r6970. These were created for the old yellow-green-red
  diff styles and look terrible now.
* Add new, minimal print styles, that replace background colors with
  text decoration (underline for inserted text, line-through for
  deleted). Motivation is the same as in r6970: light colored backgrounds
  work great on displays, but not very well in black-and-white print.
* Fixed diff styles demo (mediawiki.action.history.diff.html), updated
  with print styles and better example.

Bug: 73544
Change-Id: Ibf08fa11f84ac0cf8c7ed4da8af2b8804de6ab6f