Drop support for WikiReader

Product is no longer under active development. It stopped well over a year
ago.

Change-Id: I43cb206074e664954cda70a467fc132e91b14337
Remove SkinPerPage

Per https://gerrit.wikimedia.org/r/#/c/117810/

Change-Id: I88ef14b1ac5bd7632ce15a423486de40c4bb015a