MDL-40908 core_tag: replaced 'update' add_to_log calls with an event
MDL-40908 core_tag: replaced 'add' add_to_log call with an event
MDL-40908 core_tag: removed 'flag' add_to_log call

Removing this add_to_log call as it is an update event which
is already being triggered when this action takes place.