Revert "Add oh-my-zsh's git library but modify it to not show the branch name"

This reverts commit a337913a2b52269e4a76364c7c454e13c0544539.
Revert "Fix prompt for modified oh my zsh library files"

This reverts commit c0b0a4bb704790f0afda02a29f27c6cbcfd370f8.