Fix/hide deprecation notices in PHP/E2E tests

[tofumatt]

Summary

Addresses issue:

• WP Nightly E2E/PHP Unit tests are failing because of deprecation notice #7632

Relevant technical choices

Removed PHP Unit code that claimed to be there to prevent CI issues, but removing it caused no issues.

Rather than reach into the AMP plugin code/actions to change them around, I added an ignore for that warning hoping it gets fixed upstream (see: ampproject/amp-wp#7619).

PR Author Checklist

• My code is tested and passes existing unit tests.
• My code has an appropriate set of unit tests which all pass.
• My code is backward-compatible with WordPress 5.2 and PHP 5.6.
• My code follows the WordPress coding standards.
• My code has proper inline documentation.
• I have added a QA Brief on the issue linked above.
• I have signed the Contributor License Agreement (see https://cla.developers.google.com/).

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Code Reviewer Checklist

• Run the code.
• Ensure the acceptance criteria are satisfied.
• Reassess the implementation with the IB.
• Ensure no unrelated changes are included.
• Ensure CI checks pass.
• Check Storybook where applicable.
• Ensure there is a QA Brief.

Merge Reviewer Checklist

• Ensure the PR has the correct target branch.
• Double-check that the PR is okay to be merged.
• Ensure the corresponding issue has a ZenHub release assigned.
• Add a changelog message to the issue.

[aaemnnosttv]

Great, thanks @tofumatt 👍