Remove `wait_for_ice_gathering_complete`

[johanhelsing]

We are waiting for ice gathering completion before we start ice trickling. In theory, this should not be needed, and it's probably slowing down connection times on wasm, especially if the socket is configured with multiple stun servers. However, last I checked, if we removed the wait, nat hole punching started failing.

Solve the todo here: https://github.com/johanhelsing/matchbox/blob/d7696ad2e5f548d34c85f5c7f24efcf353b4c53b/matchbox_socket/src/webrtc_socket/wasm.rs#L130

Care should be taken to make sure that nat hole punching still works after.