gitolite: Drop openssh dependency

gitolite: Drop openssh dependency

Current dropbear is sufficient for gitolite purposes, so don't
require openssh (we don't do a dependency on either dropbear or
openssh as they are not yet drop-in replacements in terms of
packaging for the functions shared between them).  To achieve
tihs we also eliminate the dependency on ssh-keygen.  Previously
gitolite used ssh-keygen to generate fingerprints from OpenSSH
keys to ensure non-duplication of keys when processing them to
create / manage user ssh access to the git repositories.

Signed-off-by: Daniel F. Dickinson <redacted>