Staging Sites: Remove a filter that disables Jetpack staging mode for WPCOM staging sites

[fluiddot]

Fixes 7894-gh-Automattic/dotcom-forge.

Proposed changes:

• Reverts changes introduced in https://github.com/Automattic/wpcomsh/pull/1314 (wpcomsh). The hook jetpack_is_staging_site is no longer invoked, as the only place where it was triggered is the deprecated function is_staging_site. The function was deprecated as part of Staging: deprecate staging logic and replace with safe mode and dev site #37023.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

N/A

Does this pull request change what data or activity we track or use?

N/A

Testing instructions:

Note

The code is no longer used so there's no way to test it. Originally, we could test that staging badge was displayed. But following this change, the badge is no longer rendered.

[github-actions]

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Wpcomsh plugin:

• Next scheduled release: August 6, 2024.
• Scheduled code freeze: July 29, 2024.

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