NOMDL: typo, removing duplicate prevent

enrol/self/lang/en/enrol_self.php

@@ -55,7 +55,7 @@
 $string['pluginname'] = 'Self enrolment';
 $string['pluginname_desc'] = 'The self enrolment plugin allows users to choose which courses they want to participate in. The courses may be protected by an enrolment key. Internally the enrolment is done via the manual enrolmnet plugin which has to be enabled in the same course.';
 $string['requirepassword'] = 'Require enrolment key';
-$string['requirepassword_desc'] = 'Require enrolment key in new courses and prevent prevent removing of enrolment key from existing courses.';
+$string['requirepassword_desc'] = 'Require enrolment key in new courses and prevent removing of enrolment key from existing courses.';
 $string['role'] = 'Assign role';
 $string['self:config'] = 'Configure self enrol instances';
 $string['self:manage'] = 'Manage enrolled users';