Avoid re-reading tombstone data when writing tombstones

[jwilder]

Deletes read and re-write a tombstone file for a given tsm file containing series keys that are deleted. This could be improved to only write new files allow the tombstone to be immutable.

Original issue from #4977.

[jwilder]

Tombstone files are already immutable. Writing them could still be improved to avoid re-reading (or copying) existing tombstone data.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically closed because it has not had recent activity. Please reopen if this issue is still important to you. Thank you for your contributions.