Update libgit2 to 0.27.2

[mfechner]

Summary

Commit message:
Update libgit2 to 0.27.2 and removed obsolete patches from it as it is fixed upstream now.
Update devel/rubygem-rugged to 0.27.2 and took maintainer-ship for it as it is a core module required for gitlab.

Test Plan

Testbuilds were done also for:
devel/libgit2-glib
devel/py-pygit2

All patches are build, you can find all build logs:
https://pkg.fechner.net/jail.html?mastername=111amd64-gitlab

The fresh packages are tested against a new installation using:
https://gitlab.fechner.net/mfechner/Gitlab-vagrant

An old version is updated following the manual:
https://gitlab.fechner.net/mfechner/Gitlab-docu

[mat]

If both are tighly linked and need to be updated at the same time, you should add a comment at the top of both Makefile saying "Also update foo/bar".

[swills]

LGTM, would be good to add the comment @mat mentioned, and also to pet portlint by fixing the "USE_* seen before USES" warning it's giving as well.