[#137] Refactor context data retrievers

Signed-off-by: Roman Loginov <r.loginov@yadro.com>

api/handler/delete.go

@@ -281,7 +281,7 @@ func (h *handler) DeleteBucketHandler(w http.ResponseWriter, r *http.Request) {
 
 	var sessionToken *session.Container
 
-	boxData, err := layer.GetBoxData(r.Context())
+	boxData, err := middleware.GetBoxData(r.Context())
 	if err == nil {
 		sessionToken = boxData.Gate.SessionTokenForDelete()
 	}