remove_connection should not remove parent connection

When calling remove_connection in a subclass, that should not fallback
to the parent, otherwise it will remove the parent connection from the
handler.

activerecord/lib/active_record/connection_handling.rb

@@ -132,7 +132,8 @@ def connected?
       connection_handler.connected?(connection_specification_name)
     end
 
-    def remove_connection(name = connection_specification_name)
+    def remove_connection(name = nil)
+      name ||= @connection_specification_name if defined?(@connection_specification_name)
       # if removing a connection that have a pool, we reset the
       # connection_specification_name so it will use the parent
       # pool.

activerecord/test/cases/connection_adapters/connection_handler_test.rb

@@ -112,6 +112,13 @@ def test_connection_specification_name_should_fallback_to_parent
           klassA.connection_specification_name = "readonly"
           assert_equal "readonly", klassB.connection_specification_name
         end
+
+        def test_remove_connection_should_not_remove_parent
+          klass2 = Class.new(Base) { def self.name; 'klass2'; end }
+          klass2.remove_connection
+          refute_nil ActiveRecord::Base.connection.object_id
+          assert_equal klass2.connection.object_id, ActiveRecord::Base.connection.object_id
+        end
       end
     end
   end