Author: Andrew Nicols
MDL-61895 availability: Implement null provider for plugins
http://git.moodle.org/gw?p=moodle.git;a=commit;h=89ed12aa50252c4631404474bdcd01d2b7eb242f
http://github.com/moodle/moodle/commit/89ed12aa50252c4631404474bdcd01d2b7eb242f
+ 3.3 en [privacy:metadata,availability_completion]
+ 3.3 en [privacy:metadata,availability_date]
+ 3.3 en [privacy:metadata,availability_grade]
+ 3.3 en [privacy:metadata,availability_group]
+ 3.3 en [privacy:metadata,availability_grouping]
+ 3.3 en [privacy:metadata,availability_profile]