lib/deprecatedlib: enrol/manual: Fix calls to get_users_by_capability() to avoid ra

lib/deprecatedlib: enrol/manual: Fix calls to get_users_by_capability() to avoid ra

get_users_by_capability() can no longer refer to properties of role
assignments or roles, as the capability aggregate is indirect.

Fixes:
 get_teacher() - though the results will be poor, as we cannot provide
                 role.sortorder reliably
		 (used mainly by mod/workshop)
 get_course_teachers() - which seems broken for a lot of situations as
                 its default parameters still refer to old tables.

MDL-12452