portmap: remove package as it is obsolete

The upstream tarball isn't available, no releases since ten years. The
latest change to upstream git is from 2014.  Better use rpcbind for any
RPC portmapper service.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
[Thomas: make the legacy option select rpcbind, as suggested by Arnout.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>