IRGen: Stop using 'completely fragile' mode when emitting class metadata

This was a stop-gap measure until the YAML legacy type layout infrastructure
was in place.

Author: slavapestov

lib/IRGen/GenClass.cpp

@@ -376,12 +376,7 @@ namespace {
         // Lower the field type.
         auto *eltType = &IGM.getTypeInfo(type);
         if (CompletelyFragileLayout && !eltType->isFixedSize()) {
-          // For staging purposes, only do the new thing if we're going
-          // to load a YAML file describing legacy type layouts.
-          auto mode = (IGM.IRGen.Opts.DisableLegacyTypeInfo
-                       ? TypeConverter::Mode::CompletelyFragile
-                       : TypeConverter::Mode::Legacy);
-          LoweringModeScope scope(IGM, mode);
+          LoweringModeScope scope(IGM, TypeConverter::Mode::Legacy);
           eltType = &IGM.getTypeInfo(type);
         }