runtime: remove agent abstraction

This PR will delete agent abstraction and use Kata agent as the only one agent.

Fixes: #377

Signed-off-by: bin liu <bin@hyper.sh>

src/runtime/virtcontainers/factory/direct/direct_test.go

@@ -27,12 +27,11 @@ func TestTemplateFactory(t *testing.T) {
 	}
 	vmConfig := vc.VMConfig{
 		HypervisorType:   vc.MockHypervisor,
-		AgentType:        vc.NoopAgentType,
 		ProxyType:        vc.NoopProxyType,
 		HypervisorConfig: hyperConfig,
 	}
 
-	ctx := context.Background()
+	ctx := vc.WithNewAgentFunc(context.Background(), vc.NewMockAgent)
 
 	// New
 	f := New(ctx, vmConfig)