kata 2.0: delete use_vsock option and proxy abstraction

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

src/runtime/pkg/katautils/create_test.go

@@ -109,7 +109,6 @@ func newTestRuntimeConfig(dir, consolePath string, create bool) (oci.RuntimeConf
 	return oci.RuntimeConfig{
 		HypervisorType:   vc.QemuHypervisor,
 		HypervisorConfig: hypervisorConfig,
-		ProxyType:        vc.KataProxyType,
 		Console:          consolePath,
 	}, nil
 }