core_enrol_get_course_enrolment_methods is supposed to return all enrolment methods, but since manuel enrolments does not implement the get_enrol_info function it is not returned. 

Steps to recreate: 

1. Create a new external service and add the function core_enrol_get_course_enrolment_methods  
2. Create a token for the service . 
3. Create a course where where manuel enrolments are enabled 
4. Call the service eg /webservice/rest/server.php?wstoken=[token]&wsfunction=core_enrol_get_course_enrolment_methods&moodlewsrestformat=json&courseid= [courseid]'

Result: The manuel method is not returned 

Expected result: Manuel method is returned as part of the result.