API: libcrmcommon: Drop support for format=1 in xml_create_patchset()

Neither the supported values for the format argument nor their meanings
were ever documented. Pacemaker itself no longer creates patchsets of
format 1 under any circumstances, nor does it create CIBs with feature
set less than 3.0.9. So there's no longer any valid use case for
creating a format-1 patchset using xml_create_patchset().

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

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