Component subcommand should be removed in pd-ctl

[rleungx]

1. What did you do?
   show help message in pd-ctl

2. What did you expect to see?
   The component subcommand should be removed.

3. What did you see instead?

Usage:
  pd-ctl [command]

Available Commands:
  cluster     show the cluster information
  completion  Output shell completion code for the specified shell (bash)
  component   manipulate components' configs
  config      tune pd configs
  exit        exit pdctl
  health      show all node's health information of the pd cluster
  help        Help about any command
  hot         show the hotspot status of the cluster
  label       show the labels
  log         set log level
  member      show the pd member status
  operator    operator commands
  ping        show the total time spend ping the pd
  plugin      plugin commands
  region      show the region status
  scheduler   scheduler commands
  store       manipulate or query stores
  tso         parse TSO to the system and logic time

4. What version of PD are you using (pd-server -V)?
   master