chore(virtiofs): Drop feature gate EnableVirtioFsConfigVolumes

[jcanocan]

What this PR does / why we need it:

The feature has been graduated to GA. Therefore, the usage of the feature gate is not longer required to share configmaps, secrets, serviceAccounts or DownwardAPI with virtiofs.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

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• Design: A design document was considered and is present (link) or not required
• PR: The PR description is expressive enough and will help future contributors
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• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Testing: New code requires new unit tests. New features and bug fixes require at least on e2e test
• Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature / API change.
• Community: Announcement to kubevirt-dev was considered

Release note:

Remove `EnableVirtioFsConfigVolumes` feature gate references.

[kubevirt-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
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[kubevirt-bot]

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