(bug) - Remove reference to obselete manifest_dir

This commit removes references to the obselete manifest_dir puppet
configuration setting which was removed in puppet 4.x and above.

This started to happen as the latest release of rspec-puppet removed
this setting.

Author: jordanbreen28

lib/puppetlabs_spec_helper/module_spec_helper.rb

@@ -67,7 +67,6 @@ def verify_contents(subject, title, expected_lines)
 
   c.environmentpath = spec_path
   c.module_path = module_path
-  c.manifest_dir = File.join(fixture_path, 'manifests')
 
   # https://github.com/puppetlabs/rspec-puppet#strict_variables
   c.strict_variables = ENV['STRICT_VARIABLES'] != 'no'