Remove redundant namespace raising an exception

There is no need to be so explicit to raise an exception which is
defined in its same class.

src/api/lib/xpath_engine.rb

@@ -441,7 +441,7 @@ def evaluate_expr(expr, root, escape = false)
 
         if @last_key && @attribs[table][@last_key][:split]
           tvalues = value.split(@attribs[table][@last_key][:split])
-          raise XpathEngine::IllegalXpathError, 'attributes must be $NAMESPACE:$NAME' if tvalues.size != 2
+          raise IllegalXpathError, 'attributes must be $NAMESPACE:$NAME' if tvalues.size != 2
 
           @condition_values_needed.times { @condition_values << tvalues }
         elsif @last_key && @attribs[table][@last_key][:double]