GitHub: Moved / deleted resources leave dangling LFS pointer files

[shevron]

When using the GitHub backend with LFS support, if I delete a resource previously pointed to by an LFS pointer file, or change the path of an existing resource, and then call .update(), I will end up with an orphan LFS pointer file not pointing to a resource which exists in the current revision.

This can cause side effects when repositories are accessed directly via Git. When checked out, users will get the old LFS pointer files downloaded as-is without being removed or replaced by LFS.

Resources referred to by the latest revision should work correctly.