Removed support for git versions older than 2.22.

Removed support for git versions older than 2.22.

Which fixed an OOM with unlocked files.

Debian oldoldstable is the oldest version of git that git-annex needs to
support, since it's used in the amd64ancient build. That has 2.30.

At this point, the only complication git-annex for an bug in old
versions of git is that git bundle was broken before git 2.31.
That prevents git-remote-annex from working with git 2.30.

Sponsored-by: Luke T. Shumaker