fix: Use git to figure out git repo.

[mmcrockett]

I have a .git directory in my $HOME for some git hooks I have but it isn't a git repo and confuses me when I open a new terminal and forget I'm in my home but I get the 'There were more than 150 changed files.' I've included how it should look with the /tmp directory. See screenshot.

This removes the find_in_cwd_or_parent shell method in favor of just using a git command to determine. Seems simpler and more stable since it uses built-in git behaviour instead of rolling our own method.

[jeffbyrnes]

Double-checked, and indeed, this is the only use of find_in_cwd_or_parent(), so this seems like a win in terms of simplicity.

[ghthor]

Thank you @mmcrockett & @jeffbyrnes