known_classes.rb: remove DL

* lib/rdoc/known_classes.rb: reverted regression changes of rdoc
  known class.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48736 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rdoc/known_classes.rb

@@ -59,7 +59,6 @@ module RDoc
     "rb_eZeroDivError"     => "ZeroDivError",
 
     "rb_mComparable"       => "Comparable",
-    "rb_mDL"               => "DL",
     "rb_mEnumerable"       => "Enumerable",
     "rb_mErrno"            => "Errno",
     "rb_mFConst"           => "File::Constants",