* Allow `gh auth git-credential` to authenticate GitHub Gist requests
When there are stored credentials for `example.com`, allow using them to
authenticate requests to `gist.example.com` as well.
* Fix writing out of credential config
* remove unneccessary function
* actually delete
Co-authored-by: nate smith <vilmibm@github.com>
When a token such as GH_TOKEN is set through environment variables and
`~/.config/gh/hosts.yml` is non-existent, the `auth git-credential get`
command used to fail due to missing username.
Since GitHub username isn't at all required for token authentication,
use the `x-access-token` faux username instead of trying to obtain one
from a config file.
