MDL-36805 Correct docs for workshop_grade_item_update in mod_workshop

The documentation suggested that the modname field should be present on the
$workshop parameter when this is not required. It is not used in any point
in the function and the $workshop variable is never passed to another
function which may use it.

mod/workshop/lib.php

@@ -1046,7 +1046,7 @@ function workshop_get_extra_capabilities() {
  * Needed by grade_update_mod_grades() in lib/gradelib.php. Also used by
  * {@link workshop_update_grades()}.
  *
- * @param stdClass $workshop instance object with extra cmidnumber and modname property
+ * @param stdClass $workshop instance object with extra cmidnumber property
  * @param stdClass $submissiongrades data for the first grade item
  * @param stdClass $assessmentgrades data for the second grade item
  * @return void