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/Locations.hs

@@ -85,6 +85,7 @@ module Annex.Locations (
 import Data.Char
 import Data.Default
 import qualified Data.ByteString.Char8 as S8
+import qualified Data.ByteString.Lazy as L
 
 import Common
 import Key
@@ -515,7 +516,7 @@ keyFile = fromRawFilePath . keyFile'
 
 keyFile' :: Key -> RawFilePath
 keyFile' k = 
-	let b = serializeKey' k
+	let b = L.toStrict (serializeKey' k)
 	in if any (`S8.elem` b) ['&', '%', ':', '/']
 		then S8.concatMap esc b
 		else b