Revert "Experimental feature to load gemfiles from plugins"

This reverts commit 64652f98ab.

Gemfile

@@ -191,10 +191,3 @@ group :profile do
   # if you need to profile, uncomment out this line
   # gem 'rack-perftools_profiler', require: 'rack/perftools_profiler', platform: :mri_19
 end
-
-# Experiment feature to load gemfiles from plugins
-if ENV['DISCOURSE_PLUGIN_GEMFILES']
-  Dir.glob(File.join(File.dirname(__FILE__), 'plugins', '*', "Gemfile")) do |gemfile|
-    eval(IO.read(gemfile), binding)
-  end
-end