Deletion use cases clearly need some thought.

Here they are:

1. Delete a tag without deleting a manifest (who needs that?)
2. Delete a manifest without deleting a tag (impossible, should throw error)
3. Delete a manifest (and all related tags)
   • by specifying tag
   • by specifying a digest
   • warn if there are more than one related tag to be deleted (with override option)

Different interfaces:

1. http (partially exists)
2. docker cli (docker push :registry/name:tag or docker push --delete registry/name:tag)
3. docker registry cli (garbage-collect option)

There are the following issues related:
#462
#1515
#1566
#1600
#1801
#1811
#1813
#1844