Remove -enable-refleciton-builtins flag, now unnecessary

We can always potentially emit 'builtin' reflection metadata, since
that now includes imported types referenced by the module.

rdar://problem/26259668

lib/Frontend/CompilerInvocation.cpp

@@ -1271,9 +1271,6 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     if (Args.hasArg(OPT_enable_reflection_names)) {
       Opts.EnableReflectionNames = true;
     }
-    if (Args.hasArg(OPT_enable_reflection_builtins)) {
-      Opts.EnableReflectionBuiltins = true;
-    }
   }
 
   return false;