Background block supports: remove unused properties in unit tests

[ramonjd]

What? How? Why?

Rolling back changes to the background block support PHP unit tests in https://github.com/WordPress/gutenberg/pull/64328/files#diff-ce100b2b3e8a970bae81de825ea1897ec6b906a5dce500732b7aa4186fd34ff7R125 as the id does not affect the test and the code that is being tested does not take it into account at all.

The core backport is contained in WordPress/wordpress-develop#7137

Testing:

npm run test:unit:php:base -- --filter WP_Block_Supports_Background_Test

[github-actions]

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Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>
Co-authored-by: andrewserong <andrewserong@git.wordpress.org>

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[andrewserong]

LGTM, the tests pass, and it looks like the id was not necessary for these ones 👍

[github-actions]

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