Bug 1701711: Enable test case for undefined loads. r=iain

We no longer load the prototype after bug 1792228, so we don't have to support
`MObjectStaticProto` during scalar replacement. This also means scalar
replacement when loading undefined properties is now trivially supported.

Differential Revision: https://phabricator.services.mozilla.com/D161702

js/src/jit-test/tests/ion/recover-objects.js

@@ -213,9 +213,7 @@ for (var i = 0; i < max; i++) {
     dynamicSlots(i);
     testNewObject1(i);
     testNewObjectWithBranchPruning(i);
-
-    // TODO: support undefined properties in scalar replacement (bug 1701711)
-    // unknownLoad(i);
+    unknownLoad(i);
 
     // TODO: support constructors in scalar replacement (bug 1700422)
     // createThisWithTemplate(i);