[vtctldclient] Update help text for legacy shim
[vtctldclient] Update help text for legacy shim

Also remove the custom help func hack, because it turns out we don't
actually need it (thank goodness)

Signed-off-by: Andrew Mason <8a240ff75aa1467ba5eba4db0c8200b61262547e@slack-corp.com>

vitessio/vitess,vitessio/vitess,mahak/vitess,vitessio/vitess,vitessio/vitess,vitessio/vitess,vitessio/vitess,tinyspeck/vitess,mahak/vitess,mahak/vitess,mahak/vitess,mahak/vitess,mahak/vitess,tinyspeck/vitess,vitessio/vitess,vitessio/vitess,mahak/vitess,tinyspeck/vitess,tinyspeck/vitess,tinyspeck/vitess,mahak/vitess,tinyspeck/vitess,tinyspeck/vitess