Always write out nested types tables

Remove the option to switch off nested types tables. In a world where
re-entrant direct lookup will cause deserialization to fail (or worse),
disabling these tables will only lead to further instability in the
compiler.

lib/Frontend/Frontend.cpp

@@ -154,8 +154,6 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
     serializationOpts.ImportedHeader = opts.ImplicitObjCHeaderPath;
   serializationOpts.ModuleLinkName = opts.ModuleLinkName;
   serializationOpts.ExtraClangOptions = getClangImporterOptions().ExtraArgs;
-  serializationOpts.EnableNestedTypeLookupTable =
-      opts.EnableSerializationNestedTypeLookupTable;
   if (!getIRGenOptions().ForceLoadSymbolName.empty())
     serializationOpts.AutolinkForceLoad = true;