Remove wagtail-pg-search-backend (#84)

It links to a fork, not the actual repo and is part of Wagtail since 1.10 anyway.

README.md

@@ -153,7 +153,6 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 - [Wagtail Error Pages](https://gitlab.com/alexgleason/wagtailerrorpages) - Pretty, smart, customizable error pages for Wagtail.
 - [Wagtail Themes](https://github.com/moorinteractive/wagtail-themes) - Site-specific theme loader for Wagtail.
 - [Wagtail Sharing](https://github.com/cfpb/wagtail-sharing) – Easier sharing of Wagtail drafts.
-- [Wagtail Postgres Search Backend](https://github.com/leukeleu/wagtail-pg-search-backend) - PostgreSQL full text search backend for Wagtail CMS.
 - [Wagtail Gridder](https://github.com/wharton/wagtailgridder) - Grid card layout similar to Google image search results, with an expanded area for card details.
 - [Wagtail Condensed Inline Panel](https://github.com/wagtail/wagtail-condensedinlinepanel) - Drop-in replacement for Wagtail's InlinePanel suited for large number of inlines (collapsible with drag and drop support).
 - [Joyous](https://github.com/linuxsoftware/ls.joyous) - A calendar application for Wagtail.