repo delete prompts for mis-spelled repositories

[vilmibm]

I just ran gh repo delete gh-bin-upgade and then spent way too long trying to figure out why it wasn't working, only to realize i was correctly spelling gh-bin-upgrade in the prompt.

This isn't a huge problem and I recognize that only prompting for real repositories means an extra request, but it'd be nice to not be trying to type in a name that will never be accepted.