Remove dead MongoDB code (#1345)

lib/ransack/adapters.rb

@@ -2,17 +2,7 @@ module Ransack
   module Adapters
 
     def self.object_mapper
-      @object_mapper ||= instantiate_object_mapper
-    end
-
-    def self.instantiate_object_mapper
-      if defined?(::ActiveRecord::Base)
-        ActiveRecordAdapter.new
-      elsif defined?(::Mongoid)
-        MongoidAdapter.new
-      else
-        raise "Unsupported adapter"
-      end
+      @object_mapper ||= ActiveRecordAdapter.new
     end
 
     class ActiveRecordAdapter
@@ -37,28 +27,5 @@ module Ransack
         require 'ransack/adapters/active_record/ransack/context'
       end
     end
-
-    class MongoidAdapter
-      def require_constants
-        require 'ransack/adapters/mongoid/ransack/constants'
-      end
-
-      def require_adapter
-        require 'ransack/adapters/mongoid/ransack/translate'
-        require 'ransack/adapters/mongoid'
-      end
-
-      def require_context
-        require 'ransack/adapters/mongoid/ransack/visitor'
-      end
-
-      def require_nodes
-        require 'ransack/adapters/mongoid/ransack/nodes/condition'
-      end
-
-      def require_search
-        require 'ransack/adapters/mongoid/ransack/context'
-      end
-    end
   end
 end