Revert "Recompile tier1 for IFileSystem changes."

This reverts commit dd84e8624b2a88a553d15967a116288573f4ef82.
Revert "Fix the butchered previous commit."

This reverts commit 46c7527e36d06c7184ec30548800a5b3de629510.
Revert "Update IFileSystem."

This reverts commit 7200d05f09d86ff7a6a25503a35bcc51a147caf7.