git-open is supposed to be used as a git subcommand like `git open`
which requires git to function. This makes using overrides easier and
reduces useless rebuilds.
We do not use a "plugin system" for Git addons anymore, and therefore this
directory is no longer useful. Indeed that directory is way more confusing,
given that it includes more than mere Git addons, going from Bitbucket server
command-line tools to complete rewrites of Git in exotic programming languages.
Also, without this directory, the mental load of decision-making reduces a lot.
When anyone is interested in including a new git-related tool, just put it into
pkgs/applications/version-management, without apologies.
