[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_arch.sh

@@ -28,7 +28,4 @@ for filename in tmux/.*_arch.example; do
     cp $filename ${filename:0:-13}
 done
 
-for filename in vim/.*_arch.example; do
-    cp $filename ${filename:0:-13}
-done
 echo "You should now start tmux (and zsh) and nvim  for automatic plugin installation."