Use a separate branch instead of gbp-balances.toml, create separate files

[Mothblocks]

Closes #23.
Addresses, but doesn't fix #24--if you merge two PRs in quick succession from the same person, you'll still meet the race condition.

• Remove all unused stuff

[AffectedArc07]

If the action runs in 5 seconds flat that should prevent race conditions, assuming the PR is being reviewed properly. I can’t think of being able to even merge 2 PRs in the space of 5 seconds unless you have them all lined up ready to go.

[Mothblocks]

It's happened to me before, lining up PRs while I wait for their CI to pass, but something else of note is that it might not be one person merging 2 PRs, but 2 people merging PRs at the same time.

[Mothblocks]

I'm closing this specific implementation, but separate branches WILL come! @stylemistake gave me a much better solution that completely eliminates the race conditions altogether (which this doesn't do, just obscures it) that I'm going to give a shot.