message: nydusd: no need to kill self in do_exit
  We no longer rely on the event manager to exit so there is no need to
  send SIGTERM to self in order to exit.
diff: @@ -10,9 +10,6 @@ use std::sync::mpsc::{Receiver, Sender};
  use std::sync::Arc;
  use std::thread::JoinHandle;
  -use nix::sys::signal::{kill, SIGTERM};
  -use nix::unistd::Pid;
  -
  use nydus::{FsBackendType, NydusError};
  use nydus_api::http::{
  ApiError, ApiMountCmd, ApiRequest, ApiResponse, ApiResponsePayload, ApiResult, DaemonConf,
  @@ -233,9 +230,6 @@ impl ApiServer {
  ApiError::DaemonAbnormal(e.into())
  })?;
  - // Should be reliable since this Api server works under event manager.
  - kill(Pid::this(), SIGTERM).unwrap_or_else(|e| error!("Send signal error. {}", e));
  -
  Ok(ApiResponsePayload::Empty)
  }
  