Remove some redundant requires from Rakefile

All of these are in puppetlabs_spec_helper/rake_tasks.rb

moduleroot/Rakefile

@@ -1,7 +1,4 @@
 require 'puppetlabs_spec_helper/rake_tasks'
-require 'puppet-lint/tasks/puppet-lint'
-require 'puppet-syntax/tasks/puppet-syntax'
-require 'metadata-json-lint/rake_task'
 require 'puppet_blacksmith/rake_tasks'
 require 'voxpupuli/release/rake_tasks'
 require 'rubocop/rake_task'