Prior to this commit `artifact remove --all` was not supported on remote
clients.
This patch adds a new artifact API endpoint `artifact/remove` which can
either take a list of artifacts to remove or remove all artifacts by
setting all=true.
This patch removes the temporary warning message in the tunnel interface
implementation of ArtifactRm if `--all` was passed on the command line
and uses the new `artifact/remove` endpoint.
This patch also updates the `artifact remove` command both remote and
local to accept a list of artifacts to remove rather than limiting to
just one.
Signed-off-by: Lewis Roy <lewis@redhat.com>