Replace <C-C><C-C> with <C-C>

[dstein64]

Vim intentionally replaces <C-C> with <C-C><C-C>, which is reflected in the output when using -W (https://github.com/vim/vim/issues/11541).

In VimGolf, when a user enters <C-C>, the input will count as two keystrokes towards the score, showing <C-C> twice in the displayed keystrokes.

This PR updates the code to replace <C-C><C-C> with <C-C>.