Revert "Replace an deprecated constant with a new one in did_you_mean"

This reverts commit 573d9d3a4a.

test/optparse/test_did_you_mean.rb

@@ -13,7 +13,11 @@ class TestOptionParser::DidYouMean < TestOptionParser
     @opt.def_option("--bar", Integer) { |v| @bar = v }
     @opt.def_option("--baz", Integer) { |v| @baz = v }
     @formatter = ::DidYouMean.formatter
-    ::DidYouMean.formatter = ::DidYouMean::Formatter
+    case @formatter
+    when ::DidYouMean::PlainFormatter
+    else
+      ::DidYouMean.formatter = ::DidYouMean::PlainFormatter.new
+    end
   end
 
   def teardown