spacemacs/delete-current-buffer-file is defined in spacemacs-base/funcs.el.
You can override it with the desired function. Note that I just changed the prompt of the
(defun my-spacemacs/delete-current-buffer-file ()
"Removes file connected to current buffer and kills buffer."
(let ((filename (buffer-file-name))
(if (not (and filename (file-exists-p filename)))
(when (yes-or-no-p (format "Are you sure you want to delete %S? " filename))
(delete-file filename t)
(when (and (configuration-layer/package-usedp 'projectile)
(message "File '%s' successfully removed" filename)))))
(advice-add 'spacemacs/delete-current-buffer-file :override #'my-spacemacs/delete-current-buffer-file)
DISCLAIMER: I don't use spacemacs. The lisp code is currently untested. You need to test it for yourself.
Note further that there is also the very similar function
spacemacs\delete-file. You can adopt the same changes to that function if you like.
As Drew suggested you should add an enhancement issue at the spacemacs project page.