Remove deprecated plugin 'jekyll-projectlist'

My plugin 'jekyll-projectlist' has been replaced by the data file feature in Jekyll 2.0 and thus became obsolete.

Author: fhemberger

site/_docs/plugins.md

@@ -418,7 +418,6 @@ You can find a few useful plugins at the following locations:
 - [Full-text search by Pascal Widdershoven](https://github.com/PascalW/jekyll_indextank): Adds full-text search to your Jekyll site with a plugin and a bit of JavaScript.
 - [AliasGenerator by Thomas Mango](https://github.com/tsmango/jekyll_alias_generator): Generates redirect pages for posts when an alias is specified in the YAML Front Matter.
 - [Pageless Redirect Generator by Nick Quinlan](https://github.com/nquinlan/jekyll-pageless-redirects): Generates redirects based on files in the Jekyll root, with support for htaccess style redirects.
-- [Projectlist by Frederic Hemberger](https://github.com/fhemberger/jekyll-projectlist): Renders files in a directory as a single page instead of separate posts.
 - [RssGenerator by Assaf Gelber](https://github.com/agelber/jekyll-rss): Automatically creates an RSS 2.0 feed from your posts.
 - [Monthly archive generator by Shigeya Suzuki](https://github.com/shigeya/jekyll-monthly-archive-plugin): Generator and template which renders monthly archive like MovableType style, based on the work by Ilkka Laukkanen and others above.
 - [Category archive generator by Shigeya Suzuki](https://github.com/shigeya/jekyll-category-archive-plugin): Generator and template which renders category archive like MovableType style, based on Monthly archive generator.