Remove assertion for disconnect

[DivineDominion]

WebMIDIKit/Sources/WebMIDIKit/MIDIPortMap.swift

Line 70 in 6f35069

assert(port.state == .connected)

This assertion fires when you unplug a MIDI device of which a port is used.

I think removing this cause for runtime exceptions in DEBUG builds is a good fit (because the assumption that the device is still connected isn't always true!) and cannot gracefully be handled at all.

[DivineDominion]

@adamnemecek Gentle ping: what do you think about removing this?