Avoid shadowing class member "ns"

In fact validation should use the class member, and not some possibly unrelated
namespace.

Author: tautschnig

src/cbmc/bmc.cpp

@@ -642,7 +642,7 @@ void bmct::perform_symbolic_execution(
 
   if(options.get_bool_option("validate-ssa-equation"))
   {
-    symex.validate(ns, validation_modet::INVARIANT);
+    symex.validate(validation_modet::INVARIANT);
   }
 
   INVARIANT(

src/goto-symex/goto_symex.h

@@ -468,7 +468,7 @@ class goto_symext
     return _remaining_vccs;
   }
 
-  void validate(const namespacet &ns, const validation_modet vm) const
+  void validate(const validation_modet vm) const
   {
     target.validate(ns, vm);
   }