at lease print a log for "no need to check tombestone"

Feature Request

Is your feature request related to a problem? Please describe:

if the user delete tikv store not by tiup

it will just keep silent when run prune command since no any node scaling in tiup's view:

but we can see the node is tombstone by display command.

also, no way to scale-in it again by tiup:

Describe the feature you'd like:

for prune command, at least print a log for what happen when no need to check tombstone.

for scale-in,maybe we can set Offline as true and make scale-in successful when the store already tombstone

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: