Remove shadowed class declaration

It looks like one version of the class was first added [1] and then a
few days later, another was written [2]. The newer declaration appeared
lower in the file, allowing it to hide the other.

This removes the first, hidden declaration.

[1] commit 7aa493ec
    Date:   Fri Mar 1 10:36:20 2013 -0500
[2] commit f62dad2f
    Date:   Tue Mar 5 16:31:02 2013 -0500

common/lib/capa/capa/tests/response_xml_factory.py

@@ -254,27 +254,6 @@ class CustomResponseXMLFactory(ResponseXMLFactory):
         return ResponseXMLFactory.textline_input_xml(**kwargs)
 
 
-class SymbolicResponseXMLFactory(ResponseXMLFactory):
-    """ Factory for creating <symbolicresponse> XML trees """
-
-    def create_response_element(self, **kwargs):
-        cfn = kwargs.get('cfn', None)
-        answer = kwargs.get('answer', None)
-        options = kwargs.get('options', None)
-
-        response_element = etree.Element("symbolicresponse")
-        if cfn:
-            response_element.set('cfn', str(cfn))
-        if answer:
-            response_element.set('answer', str(answer))
-        if options:
-            response_element.set('options', str(options))
-        return response_element
-
-    def create_input_element(self, **kwargs):
-        return ResponseXMLFactory.textline_input_xml(**kwargs)
-
-
 class SchematicResponseXMLFactory(ResponseXMLFactory):
     """ Factory for creating <schematicresponse> XML trees """