Revert "Revert "* lib/yaml.rb: Remove Psych::EngineManager [Bug #8344]""

syck-1.0.3 gem support this imcompatible changes.

This reverts commit r46102

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46559 b2dd03c8-39d4-4d8f-98ff-823fe69b080e