docs: correct copy-pasted comments in docker client helpers

[elonfliter]

Two more doc comments are left over from the function above them and describe
the wrong thing.

• shared/services/rocketpool/client.go:568 — Client.GetDockerStatus was
  documented as "Get the current Docker image used by the given container", a
  verbatim copy of the comment on GetDockerImage at line 555. It now reads
  "Get the current Docker status of the given container", which matches the
  command it runs (docker container inspect --format={{.State.Status}}).
• shared/services/rocketpool/client.go:717 — Client.DeleteVolume was
  documented as "Deletes a container", a verbatim copy of the comment on
  RemoveContainer at line 705. It now reads "Deletes a docker volume",
  matching the command it runs (docker volume rm) and the wording of
  DeleteDockerImage immediately below it.