Fixed up a couple of incorrect response codes (#1095)

* Fixed up a couple of incorrect response codes

* Standardise all entities on 204 with no return content on successful delete

* Fix failing Fn.delete() test

api/server/trigger_delete.go

@@ -16,5 +16,5 @@ func (s *Server) handleTriggerDelete(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusNoContent, nil)
+	c.String(http.StatusNoContent, "")
 }