swift: Remove deprecated option allow_versions

[kwu83tw]

Start to log deprecation warning since Queens[1].
swift-c: Option allow_versions is deprecated. Configure the versioned_writes
middleware in the proxy-server instead. This option will be ignored in a future
release. Please refer the object versioning documentation for more
information[2].

[1] https://docs.openstack.org/releasenotes/swift/queens.html#relnotes-2-16-0-stable-queens
[2] https://docs.openstack.org/swift/latest/overview_object_versioning.html

[kwu83tw]

According to the comment from Matt, there might be a risk to deprecate this option if customer enabling 'allow_versions' before Kilo release(https://gerrit.suse.provo.cloud/#/c/5474/). Need further update from him before merging this PR.

[matthewoliver]

Thanks @kwu83tw, let me go work on an upstream patch and/or talk to other upstream cores to cover this.
Obviously this isn't an issue for green field customers, only customers pre-kilo.

I'll report back here, and on the gerrit patch once something is decided and/or landed and backported ;)

Maybe we should add the 'do not merge yet' label.

[matthewoliver]

I've raised a bug upstream to track this issue: https://bugs.launchpad.net/swift/+bug/1811044

[cmurphy]

In the ardana equivalent I've advocated for not worrying about this deprecation for now and living with it until the next round of deprecation revisions, when hopefully upstream has created a generalized solution.