MAGIC
Revert "Update git push.default to simple"

This reverts commit e53d6deb87c828c1a45cd40de6d87c987924412d.

I much prefer the behaviour of current, where if I run `git push -u origin` on a newly created branch, it pushes to origin/<branch name>, rather than simple which wants the full `git push -u origin <branch name>`. I hate repeating myself when the computer can figure it out.