fs: don't run tests for --max-duration on remote backends

This is a timing dependent test and to make it long enough so that it
would work with the remotes would make it too long for local tests.

The code paths are identical for local vs non-local so just run on
local.

This fixes the integration tests.

fs/sync/sync_test.go

@@ -993,6 +993,9 @@ func TestSyncWithUpdateOlder(t *testing.T) {
 
 // Test with a max transfer duration
 func TestSyncWithMaxDuration(t *testing.T) {
+	if *fstest.RemoteName != "" {
+		t.Skip("Skipping test on non local remote")
+	}
 	r := fstest.NewRun(t)
 	defer r.Finalise()