libvirt-domain: Drop virDomainMigrateCheckNotLocal attribute

libvirt-domain: Drop virDomainMigrateCheckNotLocal attribute

Our apibuild.py script does not cope with ATTRIBUTE_NONNULL:

Parse Error: parsing function type, ')' expected
Got token  ('name', 'char')
Last token:  ('name', 'char')
Token queue:  [('op', '*'), ('name', 'dconnuri'), ('sep', ')')]
Line 3297 end:
Makefile:2441: recipe for target '../../docs/apibuild.py.stamp' failed

Let's drop it. Moreover, up until e17ae3ccc2dbc1400 where it was
introduced we did not really care about NULL-ity of dconnuri. And
moreover the ATTRIBUTE_NONNULL merely checks for static calls
over NULL, it won't catch the dynamic ones, where a NULL is
passed by a variable at runtime.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>