Fixes Pkg.submit(): GitHub no longer stores OAuth tokens

[slundberg]

Pkg.submit() currently fails if a user has previously created a GitHub Julia Package Manager OAuth token but no longer has the token stored locally. While previously it was possible to refetch the token from GitHub, this is no longer supported: https://developer.github.com/changes/2014-12-08-removing-authorizations-token/

This PR changes the github.jl code to always create a new token (with a different fingerprint) if a local token is not found.

[wildart]

👍

[tkelman]

removing code that's broken anyway sgtm

[slundberg]

I noticed this never seemed to actually get merged. Was that intentional?

[IainNZ]

I thought this was merged too funny enough! Maybe rebase, if its still applicable?

[slundberg]

I just pulled in all the new changes from master. There were a few minor conflicts, but nothing that changed the core reason for the PR.

[tkelman]

It's preferable to rebase rather than merge for resolving conflicts, to avoid having too many unreviewable merge commits in the history.

[slundberg]

Sounds good. Now it is rebased.

[jiahao]

Thanks! let's try it.

[ivarne]

Seems like this is a prime candidate for Backporting (removing broken code).

[tkelman]

also backport 0d457dd with this

[tkelman]

Whoops, we somehow never backported #6668 to release-0.3, so there are conflicts in cherry-picking there that I don't think are worth figuring out. Taking this off the "backport pending 0.3" list, but will leave on the 0.4.1 list.