Replace fallback by error message

All bmct functionality has now been replaced by goto checker
infrastructure.

Author: peterschrammel

src/cbmc/cbmc_parse_options.cpp

@@ -669,11 +669,12 @@ int cbmc_parse_optionst::doit()
     }
   }
 
-  // fall back until everything has been ported to goto-checker
+  // We should know now which verifier to execute.
   if(verifier == nullptr)
   {
-    return bmct::do_language_agnostic_bmc(
-      options, goto_model, ui_message_handler);
+    error() << "Given combination of command line arguments not supported"
+            << eom;
+    exit(CPROVER_EXIT_USAGE_ERROR);
   }
 
   resultt result = (*verifier)();