Remove unused rename detection from updater

I renamed a file in a tap, and it did not play well with the code that relinks taps after updating: https://github.com/Homebrew/homebrew/blob/c8befa8437eb8776a18ae271f0fd68f92cfbe469/Library/Homebrew/cmd/update.rb#L56-L58

I ended up with a broken symlink left over in the formula directory.

Since we aren't actually using this code we can just remove it.