API: libcrmcommon: Drop support for format 1 in xml_apply_patchset()

There's no longer any way to create a format-1 patchset, so there's no
longer any valid use case for applying one.

This breaks API backward compatibility. Calls with a format-1 patchset
will still compile, but the return value will be NULL.

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