fff-babel-bird2: prevent error message on revert

When reverting configured settings, it is not an error if no temporary
directory for bird babel peers has been created.

Use rm -rf to prevent an error message and early exit of
configure-layer3 scripts.

Signed-off-by: Fabian Bläse <fabian@blaese.de>

src/packages/fff/fff-babel-bird2/files/lib/functions/fff/babeldaemon/bird2

@@ -68,5 +68,5 @@ babel_reload_implementation() {
 }
 
 babel_revert() {
-	rm -r /tmp/bird/fff
+	rm -rf /tmp/bird/fff
 }