tidy up string a bit.

lang/en/attendance.php

@@ -114,10 +114,9 @@ For example, if you have earned 8 of 10 points to date (80% attendance) and atte
 $string['gridcolumns'] = 'Grid columns';
 $string['groupsession'] = 'Group';
 $string['hiddensessions'] = 'Hidden sessions';
-$string['hiddensessions_help'] = '
-Session hides if course\'s start date older than its date. Change start date of course and hidden sessions will be shown.
+$string['hiddensessions_help'] = 'Sessions are hidden if they are scheduled before the course start date.
 
-You can use this feature to hide older sessions instead delete. Remember than only visible sessions using in Gradebook.';
+You can use this feature to hide older sessions instead of deleting them. Only visible sessions will appear in the Gradebook.';
 $string['identifyby'] = 'Identify student by';
 $string['includeall'] = 'Select all sessions';
 $string['includenottaken'] = 'Include not taken sessions';