Remove duplicated --help argument handling

The `parse_options_baset::main` function checks for a `--help` argument.
It calls the `help()` member function and exits rather than calling
`doit()` when this argument is specified. The duplicated code removed by
this commit was misleading because it was never reached when the
`--help` argument was specified.

Author: thomasspriggs

src/goto-bmc/goto_bmc_parse_options.cpp

@@ -30,12 +30,6 @@ int goto_bmc_parse_optionst::doit()
     return CPROVER_EXIT_SUCCESS;
   }
 
-  if(cmdline.isset("help"))
-  {
-    help();
-    return CPROVER_EXIT_SUCCESS;
-  }
-
   api_sessiont api{api_options};
 
   if(cmdline.args.size() != 1 || !api.is_goto_binary(cmdline.args[0]))