chore: remove stale Nix files (flake.nix, package.nix)

Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-019c8a85-4509-7358-9441-ddd8bc2a15c2

Author: Kosinkadink

README.md

@@ -26,12 +26,6 @@ chmod +x ComfyUI-Launcher-*.AppImage
 ./ComfyUI-Launcher-*.AppImage --no-sandbox
 ```
 
-**Nix (flake):**
-
-> ⚠️ The Nix flake (`flake.nix`) is not working currently.
-
-
-
 ## Development
 
 ### Prerequisites