nmtui: fix deletion confirmation with ESC key press
Summary
Fix confirming a profile deletion with ESC key.
Purpose
Due to a downstream patch in Debian/Ubuntu in newt library, pressing ESC key in the dialog to confirm deleting a profile has the same effect that confirming to delete. Fix it by checking explicitly if "Delete" button was pressed, and continue only in that case.
All the credits to @slowpeek that reported, investigated, found the cause, proposed the solution and tested it.
Fixes #1460 (closed).