Revert "add config for provider plugins to user Vagrantfile"

This reverts commit a024cd6206d6ee648d18e64ba3b321045469b41e because I
don't actually use those providers and API changes keep breaking this.
Revert "add redacted .vagrant.d/keys.yaml example"

This reverts commit 0cb7952582cf91675e08603f6ba75d3c151926b5.
remove .gitglobalignore
remove PATH export from .zshrc