Remove 'mediawiki.legacy.wikiprintable' module

It's a relic of simpler times, no longer used by any core skin. The
'mediawiki.legacy.commonPrint' module can be used instead.
(SkinTemplate-based skins do it automatically.)

* The 'mediawiki.legacy.wikiprintable' module has been removed.
* The skins/common/wikiprintable.css file has been deleted.
* Skin#commonPrintStylesheet has been deprecated; its return value is
  ignored.

Dependency: I96e66ff8905416bea906d40cdd72ba646399191b
Change-Id: Icbcebc8f539f7786d037b717d262684e9931aca6