search: Remove unused deprecated methods replaced by MW Services
The following methods deprecated in .27 and no longer used have
been removed;
- SearchEngine::userNamespaces()
https://codesearch.wmflabs.org/search/?q=%3A%3AuserNamespaces&i=nope&files=&repos=
- SearchEngine::namespacesAsText()
https://codesearch.wmflabs.org/search/?q=%3A%3AnamespacesAsText&i=nope&files=&repos=
- SearchEngine::create()
https://codesearch.wmflabs.org/search/?q=SearchEngine%3A%3Acreate&i=nope&files=&repos=
- SearchEngine::getSearchTypes()
https://codesearch.wmflabs.org/search/?q=%3A%3AgetSearchTypes&i=nope&files=&repos=
- SearchEngine::getNearMatch()
https://codesearch.wmflabs.org/search/?q=SearchEngine%3A%3AgetNearMatch%5C(&i=nope&files=&repos=
Also, replace deprecated use of searchableNamespaces() in SearchEngine.
Bug: T220656
Change-Id: I330fbfea158f70b2328da7c850fdb833e39b6c7d