Remove dependency on MediaWiki core skins.vector.styles module

Also removed redundant 'line-height' declaration on blockquote
(it's already set to that from the inherited styles).

This is needed so that we can remove the Vector path from the global
Less import path list in MediaWiki core.

Change-Id: I6514a3418d3cd074458f83aa81065dba3ef00fdd
Merge "Remove dependency on MediaWiki core skins.vector.styles module"