Thanks to mitaliajgaonkar for helping find the solution. It involves editing the source code in the following way:
Navigate to where your Qlik Sense program files are, and find the file:
Copy this file and save it somewhere else as a backup in case anything goes wrong. Then open the file and find the string tid="MenuBtn".
This string is in a <button> tag which you will need to delete as well as the <div> around the button. Once this has been removed you will no longer see the dropdown for Dev Hub, Help, and About on any account. Now, to get to the dev hub you just append "/dev-hub/" to the end of your url. Keep in mind that if you upgrade, you will have to redo this change.
At version 3.1.* you need to add the following code to the stylesheet at C:\Program Files\Qlik\Sense\Client\hub\hub.css
But be aware that this only hides the buton. It's still available when using ~/dev-hub/ in your URL.
So therefore you need to block the URL by firewall for instance.
Or deface / redirect it by putting this in the meta part of the file at location C:\Program Files\Qlik\Sense\Client\dev-hub.html
<meta http-equiv="refresh" content="0; URL='xxxxxxxxxxxxx'" />
Also make sure you set the security rules properly with read only on Extensions for instance.