Rebind `nrepl-interrupt` to `C-c C-c`

`C-c C-c` is the gold interrupt standard in Emacs (from `comint-mode`)
and has a nice mnemonic relation to the Unix shell's interrupt `C-c` key combo.

It makes perfect sense to me to use `C-c C-c` in both `nrepl-mode` and `nrepl-interaction-mode` and to preserve the `C-c C-b` for other functionality down the road.