luks2: Strip dashes off of the UUID

luks2: Strip dashes off of the UUID

The UUID header for LUKS2 uses a format with dashes, same as for
LUKS(1). But while we strip these dashes for the latter, we don't for
the former. This isn't wrong per se, but it's definitely inconsistent
for users as they need to use the dashed format for LUKS2 and the
non-dashed format for LUKS when e.g. calling "cryptomount -u $UUID".

Fix this inconsistency by stripping dashes off of the LUKS2 UUID.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>