Refactor: libcrmcommon: Drop version arg from pcmk__digest_xml()

Unconditionally use v2 digests except for operations and on-disk CIBs.
We no longer support rolling upgrades from < 2.0.0, so we should never
create v1 digests in other contexts.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>