Returns a list of users from the client server who are enrolled in our course
Suitable instance of enrol_mnet must be created in the course. This method will not
return any information about the enrolments in courses that are not available for
remote enrolment, even if their users are enrolled into them via other plugin
(note the difference from {@link self::user_enrolments()}).
This method will return enrolment information for users from hosts regardless
the enrolment plugin. It does not matter if the user was enrolled remotely by
their admin or locally. Once the course is available for remote enrolments, we
will tell them everything about their users.
In Moodle 1.x the returned array used to be indexed by username. The side effect
of MDL-19219 fix is that we do not need to use such index and therefore we can
return all enrolment records. MNet clients 1.x will only use the last record for
the student, if she is enrolled via multiple plugins.