isdtp is a salesforce classic standard parameter which will give us functionality to work with header and sidebars. isdtp has no relation with salesforce lightning so dude you are not able to set it using
$A.get("e.force:navigateToURL");
url event.
isdtp url parameter does not allow to switch to lightning so you are not able to use it.
For more please follow these links:
https://developer.salesforce.com/forums/?id=906F0000000DDWFIA4 Visualforce embedded report - isdtp parameter options
May this will help you.
Best