Maildir: Temporarily disable transfer type
Maildir: Temporarily disable transfer type

refs #7228

Remove maildir as a transfer type until it is better supported and doesn't
always break.

eckardm/archivematica,michal-ruzicka/archivematica,michal-ruzicka/archivematica,sevein/archivematica,artefactual/archivematica,artefactual/archivematica,eckardm/archivematica,sevein/archivematica,eckardm/archivematica,michal-ruzicka/archivematica,sevein/archivematica,artefactual/archivematica,artefactual/archivematica,eckardm/archivematica,sevein/archivematica,michal-ruzicka/archivematica