Update open-webui.yml

[Vdauphin]

remove deprecated https://docs.openwebui.com/getting-started/env-configuration/#ollama_api_base_url

First of all, thank you for your contribution! 😄

☑️ Self Check before Merge

• I have tested the template using the method described in README.md thoroughly
• I have ensured that I put as much default values as possible (except passwords) to ensure minimum effort required for end users to get started.
• I have ensured that I am not using the "latest" tag as this tag is dynamically changing and might break the one-click app. Use a fixed version.
• I have made sure that instructions.start and instructions.end are clear and self-explanatory.
• Icon is added as a png file to the logos directory.