Gen 2: Allow event tradebacks on gen 2

With this change, you can use something as Lovely Kiss Snorlax with Double-Edge.
You could get the lovely kiss Snorlax from event, trade it to Gen 1 as lovely kiss existed, teach it Double-Edge through TM and trade it back to Gen 2.
Tested that it doesn't break gens 3-6 with Charmander with howl and body slam (gen 4 event, gen 3 TM).