Conc::Map - MRI backend can't use native Hash#value?

Hash#value? bumps internal hash iteration level and under certain
circumstances might yield GVL. This in turn exposes users to
potential "modification during iteration" errors.

Author: thedarkone

lib/concurrent/collection/map/non_concurrent_map_backend.rb

@@ -76,10 +76,6 @@ def key?(key)
         @backend.key?(key)
       end
 
-      def value?(value)
-        @backend.value?(value)
-      end
-
       def delete(key)
         @backend.delete(key)
       end

lib/concurrent/collection/map/synchronized_map_backend.rb

@@ -53,10 +53,6 @@ def key?(key)
         synchronize { super }
       end
 
-      def value?(value)
-        synchronize { super }
-      end
-
       def delete(key)
         synchronize { super }
       end

lib/concurrent/map.rb

@@ -149,7 +149,7 @@ def value?(value)
         return true if value.equal?(v)
       end
       false
-    end unless method_defined?(:value?)
+    end
 
     def keys
       arr = []