With kata containers moving to 2.0, (hybrid-)vsock will be the only
way to directly communicate between host and agent.
And kata-proxy as additional component to handle the multiplexing on
serial port is also no longer needed.
Cleaning up related unit tests, and also add another mock socket type
`MockHybridVSock` to deal with ttrpc-based hybrid-vsock mock server.
Fixes: #389
Signed-off-by: Penny Zheng penny.zheng@arm.com