Remove all versions for backups when using S3

[hakman]

Fixes #325

[hakman]

@justinsb @johngmyers

[johngmyers]

/lgtm

[justinsb]

Thanks for finding & fixing this. Because this is existing behaviour (vs a regression), I propose we cut kops 1.16.3, 1.17.0 and then get this into the next 1.18 prerelease (likely this weekend). Because we have the IAM changes already in 1.16.3 and 1.17.0, users can opt in, and then we can make it the default in 1.17.1 (and also in 1.16.4?)

[hakman]

Sounds good to me.
Maybe 1.18 can be beta.1 (I think it's time) and also cut the the branch for it.

[johngmyers]

Now that 1.16.3 and 1.17.0 have released perhaps we should update the vendoring.

[justinsb]

@johngmyers it's a good idea to pin to e.g. 1.17.0, I don't think it's going to change anything (I think) so I propose we do that in a follow-on PR, so we can start to get this tested e2e!

/approve
/lgtm

[justinsb]

I updated the vendored kops version in #329; doesn't seem to be any code changes to the VFS code directly, but looks like some other libraries get updated.