Kill off [_]RawOptionSetType

Now that we are using OptionSetType for option sets, all the support for
doing things the old way can die.

Note: the fix-it that used to apply to RawOptionSetType, it seemed to me,
should still apply to OptionSetType, so I switched it over instead of
removing it.

Swift SVN r29066

lib/Frontend/CompilerInvocation.cpp

@@ -632,9 +632,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
 
   Opts.EnableInterfaceTypeMangling |= Args.hasArg(OPT_enable_interface_type_mangling);
 
-  Opts.ImportNSOptionsAsOptionSetType |=
-    Args.hasArg(OPT_import_ns_options_as_option_set_type);
-
   Opts.DisableAvailabilityChecking |=
       Args.hasArg(OPT_disable_availability_checking);