docs: put screenshots for Chrome extension in correct place

[ligfx]

Checked, no repos use the chrome_extension/ assets or the developer mode screenshots.

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Note

Low Risk
Docs/assets-only change with no runtime impact; the diff shows no code modifications.

Overview
This PR is effectively a no-op: the provided diff indicates a file removal to /dev/null and there are no tracked references to Chrome extension assets, screenshots, or “developer mode” content in the repo snapshot.

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[asikowitz]

Are you sure they're not being used here: https://docs.datahub.com/docs/managed-datahub/chrome-extension? For example, one of the images has source https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/saas/extension_view_in_looker.png

[ligfx]

@asikowitz right, it's using the images under saas/, not the ones under chrome_extension/