It seems impossible. When a move is deleted the field in the data structure is set to zero, so no trace of the previous move remains.
Wow. I just found out that the EXACT SAME THING happened to my FireRed charizard. He knew Cut, I had him forget it to move him to Diamond, then I bred him with Ditto (in Diamond) and he had a baby Charmander that knew Cut. Strange... Apparently this IS possible...