MDL-40697 core_grades: changed user_graded event name
MDL-40697 core_grades: removed existing user_graded event triggers
MDL-40697 core_grades: trigger the user_graded event
MDL-40697 core_grades: trigger the grade_deleted event
MDL-40697 core: added more unit tests for the user_graded event
MDL-40697 core: added unit test for grade_deleted event
MDL-40697 mod_*: fixed unit tests so they pass