How to delete an app that keeps the phone from successfully booting up?
As I've pointed out in my comment on your question, this rather is an XY problem – your real issue is to delete that app.

That's what safe-mode is intended for. You can find a detailed tutorial at HowToGeek, describing how to enter safe-mode, and what steps to take from there. I'll try to sum it up in a short list here:


Usually you'll find an option to boot into safe-mode when invoking the power menu (long-press the Power button while the device is operating in "normal mode" – not an option for you, as your device is stuck already. Refer to our safe-mode tag-wiki for alternatives: usually it's long-pressing power to switch it on, and as soon as the logo appears press vol+ and vol- simultaneously. Hold them pressed until you see the text "Safe Mode" appearing in the lower-left corner of the screen
While in safe mode, none of the user-apps will be executed – they will be disabled. So your app should not be able to "intervene" here
System stuff is still fully operational, so go to Settings › Apps, scroll to your app, open its entry, and from that screen uninstall it


Problem solved – hopefully :)