chore!: remove the pre-NixOS dotfiles tree

The flake and its modules now own every config these files provided;
they remain in history for reference while the migration finishes.

BREAKING CHANGE: `.config/`, `.gitconfig`, and `.github/` no longer exist
at the repository root. A checkout that deploys this tree into `$HOME`
will delete the live configs it previously installed.

.gitignore

@@ -1,9 +1 @@
-.dotfiles
-.DS_Store
-*.swp
-*.swo
-*~
-Thumbs.db
-**/__pycache__
-.config/fish/conf.d/secrets.fish
 /reference/