unused: When large files are checked right into git, avoid buffering their contents in memory.

This makes it a little bit slower since it has to check file size,
but worth it to fix a potential memory use problem.

This commit was sponsored by Fernando Jimenez on Patreon.

Command/Unused.hs

@@ -25,7 +25,6 @@ import qualified Git.LsFiles as LsFiles
 import qualified Git.DiffTree as DiffTree
 import qualified Remote
 import qualified Annex.Branch
-import Annex.Link
 import Annex.CatFile
 import Annex.WorkTree
 import Types.RefSpec
@@ -272,8 +271,7 @@ withKeysReferencedDiff a getdiff extractsha = do
   	go d = do
 		let sha = extractsha d
 		unless (sha == nullSha) $
-			(parseLinkOrPointer <$> catObject sha)
-				>>= maybe noop a
+			catKey sha >>= maybe noop a
 
 {- Filters out keys that have an associated file that's not modified. -}
 associatedFilesFilter :: [Key] -> Annex [Key]