Don't force a keyfile

When the keyfile passed to paramiko doesn't exist connecting to the
remote device will fail, to fix that simply remove it. Specifying it has
very little value given paramiko should search for private keys in .ssh
by default.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D5251