[SETUP] Remove defunct vim subtree and stale subtree metadata

The vim/ subtree had no tracked files or directory and its setup loops
were dead. The tmux/zsh subtrees have not been synced upstream since 2017; all
changes are now direct commits. Delete .gittrees and the vim example-linking
loops.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

setup_mac.sh

@@ -26,10 +26,6 @@ for filename in tmux/.*_mac.example(N); do
     gln -Tsvf $PWD/$filename $PWD/${filename:0:-12}
 done
 
-for filename in vim/.*_mac.example(N); do
-    gln -Tsvf $PWD/$filename $PWD/${filename:0:-12}
-done
-
 open fonts/*.ttf
 
 echo "You should now start tmux (and zsh) and nvim for automatic plugin installation."