Let allies cancel out of Bard's ult

When Bard hits an ally with his ult, temporarily replace their ability keys with a "leave stasis" ability, like Zyra's passive does when she dies.

This does two things: it gives Bard a small buff which might get him closer to a 50% win rate, since it now affects allies for whatever they consider the optimal length of time rather than always for the full 2.5 seconds, and it tones down one of the game's "I'm helping!" mechanics, since now a Bard ult is less capable of actively sabotaging your own team.