Revert "cache the serialization of a Key"

This reverts commit 4536c93bb2.

That broke Read/Show of a Key, and unfortunately Key is read in at least
one place; the GitAnnexDistribution data type.

It would be worth bringing this optimisation back, but it would need
either a custom Read/Show instance that preserves back-compat, or
wrapping Key in a data type that contains the serialization, or changing
how GitAnnexDistribution is serialized.

Also, the Eq instance would need to compare keys with and without a
cached seralization the same.

Annex/DirHashes.hs

@@ -65,14 +65,14 @@ hashDirs (HashLevels 1) sz s = addTrailingPathSeparator $ take sz s
 hashDirs _ sz s = addTrailingPathSeparator $ take sz s </> drop sz s
 
 hashDirLower :: HashLevels -> Hasher
-hashDirLower n k = hashDirs n 3 $ take 6 $ show $ md5s $ serializeKey' $ nonChunkKey k
+hashDirLower n k = hashDirs n 3 $ take 6 $ show $ md5 $ serializeKey' $ nonChunkKey k
 
 {- This was originally using Data.Hash.MD5 from MissingH. This new version
 - is faster, but ugly as it has to replicate the 4 Word32's that produced. -}
 hashDirMixed :: HashLevels -> Hasher
 hashDirMixed n k = hashDirs n 2 $ take 4 $ concatMap display_32bits_as_dir $
 	encodeWord32 $ map fromIntegral $ Data.ByteArray.unpack $
-		Utility.Hash.md5s $ serializeKey' $ nonChunkKey k
+		Utility.Hash.md5 $ serializeKey' $ nonChunkKey k
   where
 	encodeWord32 (b1:b2:b3:b4:rest) =
 		(shiftL b4 24 .|. shiftL b3 16 .|. shiftL b2 8 .|. b1)