Remove methods from SpecialPage deprecated in 1.17 and 1.18

No longer used in core or Gerrit extensions. Some patches have been
submitted to remove the last usages. For details see:
* https://gerrit.wikimedia.org/r/#/q/status:open+topic:replace-deprecated,n,z
* https://gerrit.wikimedia.org/r/#/q/status:merged+topic:replace-deprecated,n,z

- SpecialPage::__call() (deprecated in 1.17)
- SpecialPage::executePath() (deprecated in 1.18)
- SpecialPage::exists() (deprecated in 1.18)
- SpecialPage::file() (deprecated in 1.18)
- SpecialPage::func() (deprecated in 1.18)
- SpecialPage::getGroup() (deprecated in 1.18)
- SpecialPage::getPage() (deprecated in 1.18)
- SpecialPage::getPageByAlias() (deprecated in 1.18)
- SpecialPage::getLocalNameFor() (deprecated in 1.18)
- SpecialPage::getRegularPages() (deprecated in 1.18)
- SpecialPage::getRestrictedPages() (deprecated in 1.18)
- SpecialPage::getTitleForAlias() (deprecated in 1.18)
- SpecialPage::getUsablePages() (deprecated in 1.18)
- SpecialPage::includable() (deprecated in 1.18)
- SpecialPage::init()
- SpecialPage::initAliasList() (deprecated in 1.18)
- SpecialPage::initList() (deprecated in 1.18)
- SpecialPage::name() (deprecated in 1.18)
- SpecialPage::removePage() (deprecated in 1.18)
- SpecialPage::resolveAlias() (deprecated in 1.18)
- SpecialPage::resolveAliasWithSubpage() (deprecated in 1.18)
- SpecialPage::restriction() (deprecated in 1.18)
- SpecialPage::setGroup() (deprecated in 1.18)

Change-Id: I5122f0f23255bc1e8b63a7329a6d1653899b7f59
Merge "Remove methods from SpecialPage deprecated in 1.17 and 1.18"