fix get_module declaration

The declaration and the definition of get_module have diverged, making the
function unusable.

Author: kroening

src/util/get_module.h

@@ -14,13 +14,13 @@ Author: Daniel Kroening, [email protected]
 
 #include <string>
 
-class symbol_tablet;
+class symbol_table_baset;
 class message_handlert;
 class symbolt;
 
 const symbolt &get_module(
-  const symbol_tablet &symbol_table,
+  const symbol_table_baset &,
   const std::string &module,
-  message_handlert &message_handler);
+  message_handlert &);
 
 #endif // CPROVER_UTIL_GET_MODULE_H