Revert "Load gems of assets group before of precompile"

This reverts commit bbc19aa.
The assets group doesn't exist anymore in Rails default Gemfile

Author: guilleiguaran

lib/sprockets/rails/task.rb

@@ -12,8 +12,6 @@ def define
           # Override this task change the loaded dependencies
           desc "Load asset compile environment"
           task :environment do
-            # Load gems in assets group of Gemfile
-            Bundler.require(:assets) if defined?(Bundler)
             # Load full Rails environment by default
             Rake::Task['environment'].invoke
           end