repository: Remove empty cleanup functions in tests

TestRepository and its variants always returned no-op cleanup functions.
If they ever do need to do cleanup, using testing.T.Cleanup is easier
than passing these functions around.

internal/restorer/restorer_unix_test.go

@@ -16,8 +16,7 @@ import (
 )
 
 func TestRestorerRestoreEmptyHardlinkedFileds(t *testing.T) {
-	repo, cleanup := repository.TestRepository(t)
-	defer cleanup()
+	repo := repository.TestRepository(t)
 
 	sn, _ := saveSnapshot(t, repo, Snapshot{
 		Nodes: map[string]Node{