Hide WebRTC bots on IRC

[afranke]

When someone starts a call, a bot joins the room. That bot has a ghost on the IRC side, which is unnecessary. The bridge could “filter it out”.

[Mikaela]

I think this could possibly be called as duplicate of #47 which would be a better (or the) solution.

[kegsay]

The bridge doesn't know it's a bot, needs additional info from Matrix.

[Half-Shot]

Closing this as I don't think this is an actionable item. Separately, the verto bridge isn't in use anymore.