remove redundant event source logic

[hannahblair]

Description

The old event source logic was mistakenly added back in in #8181. This removes that.

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Tests

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[gradio-pr-bot]

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Install Gradio from this PR

pip install https://gradio-builds.s3.amazonaws.com/53e277814c0551d093d9ed55c8630c3e04ca7633/gradio-4.28.3-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@53e277814c0551d093d9ed55c8630c3e04ca7633#subdirectory=client/python"

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/client	minor
gradio	minor

• [ ] Maintainers can select this checkbox to manually select packages to update.

With the following changelog entry.

remove redundant event source logic

Maintainers or the PR author can modify the PR title to modify this entry.

#### Something isn't right?

- Maintainers can change the version label to modify the version bump. - If the bot has failed to detect any changes, or if this pull request needs to update multiple packages to different versions or requires a more comprehensive changelog entry, maintainers can [update the changelog file directly](https://github.com/gradio-app/gradio/edit/remove-old-evtsource/.changeset/gold-frogs-sniff.md).