Deprecate & remove System.Linux.Btrfs.ByteString

[redneb]

System.Linux.Btrfs.ByteString was created as an alternative to System.Linux.Btrfs, which uses FilePath to represent file paths. The problem with FilePath is that it requires for file paths to be encoded/decoded according to the current locale. This could potentially cause issues when a raw path contains byte sequences that are not valid according to the encoding used.

Fortunately, GHC provides a good solution to this issue via its file system encoding, which ensures that in a decode/encode cycle RawFilePath -> FilePath -> RawFilePath there will be no loss of information.

Therefore, I will drop System.Linux.Btrfs.ByteString from this library, unless I hear a good argument in favor of keeping it.