[MIE-1434] add verb to deleteSpecificActivity endpoint response

I add the deleted activity verb to the response to be able to know from front-end, the verb of the activity we need to remove. 
The verb object has that structure with data property and created or updated timestamp. On modules activitystreams the response of delete and post endpoint pass through some filter methods and parser that assume that the actor,object and verb have the data property so I kept the same structure to avoid this problems.