refactor: use f-strings in dynamips nodes

gns3server/compute/dynamips/nodes/c2691.py

@@ -102,9 +102,5 @@ class C2691(Router):
 
         await self._hypervisor.send(f'c2691 set_iomem "{self._name}" {iomem}')
 
-        log.info(
-            'Router "{name}" [{id}]: I/O memory updated from {old_iomem}% to {new_iomem}%'.format(
-                name=self._name, id=self._id, old_iomem=self._iomem, new_iomem=iomem
-            )
-        )
+        log.info(f'Router "{self._name}" [{self._id}]: I/O memory updated from {self._iomem}% to {iomem}%')
         self._iomem = iomem