open-webui Removed version syntax as its no longer needed per Docker Docs

Pull Request Checklist

[x] Target branch: Pull requests should target the dev branch.
[x] Description: Briefly describe the changes in this pull request.
[x] Changelog: Ensure a changelog entry following the format of Keep a Changelog is added at the bottom of the PR description.
[x] Documentation: Have you updated relevant documentation Open WebUI Docs, or other documentation sources?
[x] Dependencies: Are there any new dependencies? Have you updated the dependency versions in the documentation?
[x] Testing: Have you written and run sufficient tests for the changes?
[x] Code Review: Have you self-reviewed your code and addressed any coding standard issues?

Description

Removes version: syntax in docker-compose files. If left in, it throws an obsolete warning. I removed them from the docker-compose files to reduce unnecessary warnings and to keep the code up to current standards. See Version top-level element (obsolete) for reference.