[NFC][CAS] Cleanup CAS-based file system initialization

Author: cachemeifyoucan

lib/Frontend/CachingUtils.cpp

@@ -380,15 +380,6 @@ Expected<IntrusiveRefCntPtr<vfs::FileSystem>>
 createCASFileSystem(ObjectStore &CAS, ArrayRef<std::string> FSRoots,
                     ArrayRef<std::string> IncludeTrees) {
   assert(!FSRoots.empty() || !IncludeTrees.empty() && "no root ID provided");
-  if (FSRoots.size() == 1 && IncludeTrees.empty()) {
-    auto ID = CAS.parseID(FSRoots.front());
-    if (!ID)
-      return ID.takeError();
-    auto Ref = CAS.getReference(*ID);
-    if (!Ref)
-      return createCASObjectNotFoundError(*ID);
-  }
-
   auto NewRoot = mergeCASFileSystem(CAS, FSRoots);
   if (!NewRoot)
     return NewRoot.takeError();