Add DISTINCT to the SQL call to remove duplicate ID numbers

This removes the following error message when debugging is turned on. We have the same role with the moodle/course:manageactivities capability in two different contexts. Adding DISTINCT removes the duplicate row.

Did you remember to make the first column something unique in your call to get_records? Duplicate value '3' found in column 'id'.

    line 1005 of /lib/dml/mysqli_native_moodle_database.php: call to debugging()
    line 162 of /mod/equella/common/lib.php: call to mysqli_native_moodle_database->get_records_sql()
    line 83 of /mod/equella/settings.php: call to get_all_editing_roles()
    line 89 of /lib/classes/plugininfo/mod.php: call to include()
    line 35 of /admin/settings/plugins.php: call to core\plugininfo\mod->load_settings()
    line 6389 of /lib/adminlib.php: call to require()
    line 51 of /admin/settings.php: call to admin_get_root()