prune: no longer disable automatic index updates

this allows prune to resume an interrupted prune run.

cmd/restic/cmd_prune.go

@@ -162,9 +162,6 @@ func runPrune(ctx context.Context, opts PruneOptions, gopts GlobalOptions, term
 }
 
 func runPruneWithRepo(ctx context.Context, opts PruneOptions, gopts GlobalOptions, repo *repository.Repository, ignoreSnapshots restic.IDSet, term *termstatus.Terminal) error {
-	// we do not need index updates while pruning!
-	repo.DisableAutoIndexUpdate()
-
 	if repo.Cache == nil {
 		Print("warning: running prune without a cache, this may be very slow!\n")
 	}