vmm: Move VM shutdown event to Vmm::vm_shutdown

Signed-off-by: Bo Chen <chen.bo@intel.com>

vmm/src/vm.rs

@@ -1397,8 +1397,6 @@ impl Vm {
         }
         *state = new_state;
 
-        event!("vm", "shutdown");
-
         Ok(())
     }