Clean up direct mode cache and mapping info when dropping keys.

These files were left behind, and made getKeysPresent find keys that were
not present. It would be expensive to make getKeysPresent check that the
actual key files are present (it just lists the directories). But that's not
needed if we just clean up the stale cache and mapping files.

To handle systems that were in direct mode and got switched back with stale
direct mode files, made cleanObjectLoc remove all files in the key's directory.

git annex unused will still list keys that are gone but for which the stale
direct mode files exists. To deal with that, made dropunused remove the key's
directory even if the key does not seem to be present.

Annex/Content/Direct.hs

@@ -15,7 +15,6 @@ module Annex.Content.Direct (
 	recordedCache,
 	compareCache,
 	writeCache,
-	removeCache,
 	genCache,
 	toCache,
 	Cache(..),
@@ -129,12 +128,6 @@ writeCache key cache = withCacheFile key $ \cachefile -> do
 	createContentDir cachefile
 	liftIO $ writeFile cachefile $ showCache cache
 
-{- Removes a cache. -}
-removeCache :: Key -> Annex ()
-removeCache key = withCacheFile key $ \f -> do
-	createContentDir f -- also thaws directory
-	liftIO $ nukeFile f
-
 {- Cache a file's inode, size, and modification time to determine if it's
  - been changed. -}
 data Cache = Cache FileID FileOffset EpochTime