MDL-36014 cohorts: fix string names

Cohort capabilities are defined in lang/en/roles.php, remove(rename) the capability-styled strings

AMOS BEGIN
 CPY [cohort:assign,core_assign],[assigncohorts,core_assign]
AMOS END

cohort/assign.php

@@ -62,7 +62,7 @@
 }
 $PAGE->navbar->add(get_string('assign', 'cohort'));
 
-$PAGE->set_title(get_string('cohort:assign', 'cohort'));
+$PAGE->set_title(get_string('assigncohorts', 'cohort'));
 $PAGE->set_heading($COURSE->fullname);
 
 echo $OUTPUT->header();

lang/en/cohort.php

@@ -36,9 +36,7 @@
 $string['cohort'] = 'Cohort';
 $string['cohorts'] = 'Cohorts';
 $string['cohortsin'] = '{$a}: available cohorts';
-$string['cohort:assign'] = 'Assign cohort members';
-$string['cohort:manage'] = 'Manage cohorts';
-$string['cohort:view'] = 'Use cohorts and view members';
+$string['assigncohorts'] = 'Assign cohort members';
 $string['component'] = 'Source';
 $string['contextnotfound'] = 'Context <b>{$a}</b> not found or you don\'t have permission to create a cohort there. The default context will be used.';
 $string['csvcontainserrors'] = 'Errors were found in CSV data. See details below.';
@@ -84,4 +82,4 @@
 * The first record contains a list of fieldnames defining the format of the rest of the file
 * Required fieldname is name
 * Optional fieldnames are idnumber, description, descriptionformat, context, category, category_id, category_idnumber, category_path
-';
+';