[turbofan] Remove dead branch

A prototype map can't be deprecated.

Bug: v8:7790
Change-Id: I26ef4d9648985417212dcf4df0d47568861e9bc2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2196124
Auto-Submit: Georg Neis <neis@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67738}

src/compiler/access-info.cc

@@ -587,11 +587,7 @@ PropertyAccessInfo AccessInfoFactory::ComputePropertyAccessInfo(
       }
     }
     Handle<JSObject> map_prototype(JSObject::cast(map->prototype()), isolate());
-    if (map_prototype->map().is_deprecated()) {
-      // Try to migrate the prototype object so we don't embed the deprecated
-      // map into the optimized code.
-      JSObject::TryMigrateInstance(isolate(), map_prototype);
-    }
+    CHECK(!map_prototype->map().is_deprecated());
     map = handle(map_prototype->map(), isolate());
     holder = map_prototype;