Remove unnecessary git binary path juggling

dotfiles/gittum/bin/setup

 #!/bin/bash
 
-git_binary=$(which git)
-if [[ -x "$HOME/bin/git" ]]; then
-    git_binary="$HOME/bin/git"
 gitver=$(git --version | cut -d ' ' -f 3)
 if [[ "x$gitver" > "x1.8" ]]; then
     tilde='~'