Remove messaging code

[tomlinton]

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• [x] Code contains relevant tests for the problem you are solving
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Description:

• Messaging code now lives in origin-box so I've removed it and added a README letting people know

[franckc]

@crazybuster @micahalcorn FYI the messaging server code was moved from bridge repo to origin-box: https://github.com/OriginProtocol/origin-box/tree/master/origin-messaging This is a good step towards mono-repo... :)