Deprecate the workaround token feature as well and then eventually remove it

[asvoboda]

We should probably deprecate the workaround token feature as well and then eventually remove it. Should simplify the code a decent amount, since there's logic to specifically detect if push restrictions are enabled.

Originally posted by @bluekeyes in https://github.com/palantir/bulldozer/pull/171#issuecomment-595859817

[brendan-donegan]

Hi,

Just a note that some users of Bulldozer (us, for example) are stuck on infrastructure that doesn't support adding the app as a collaborator, e.g. older versions of Github Enterprise. We could of course pin our Bulldozer version to avoid this, but just wanted to let you know this was the case.

[bluekeyes]

Thanks for highlighting this. I think the main thing here is to update the documentation and code to clearly indicate that this property is deprecated and only used with older GitHub Enterprise versions. I don't expect to remove the feature in the near future.

For planning, can you share what version of GitHub Enterprise you are currently using or about how far behind the latest release you usually are?

[brendan-donegan]

I believe we missed it by a whisker, we're on 2.18 at the moment and the supporting feature was added in 2.19 (although because we need the Terraform provider to be updated as well, we'd need to update that to 2.50)

[brendan-donegan]

See https://github.com/terraform-providers/terraform-provider-github/blob/90eae460c07bfc332140262c3398525f33d47fc9/CHANGELOG.md#250-march-30-2020