Fix Stylelint error for rule: `selector-type-no-unknown`

[brookewp]

Related to: #67467

Proposed Changes

Original PR for this was closed due to issues with the branch #67996

There was only one error for selector-type-no-unknown when running yarn lint:css. Since the selector was broken and we have blocks now, the CSS isn't being used. So to fix this error, I'm proposing to remove the CSS which will keep trunk looking the same while removing the stylelint error.

Testing Instructions

1. TeamCity
2. Add Twitter link to post and see it is still left-aligned in Reader

[github-actions[bot]]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-44380

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https://calypso.live?image=registry.a8c.com/calypso/app:build-44380&env=jetpack

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[manzoorwanijk]

There are 2 more places with the same error:

client/components/advanced-credentials/style.scss
 68:8  ✖  Unexpected unknown type selector "first-child"  selector-type-no-unknown

client/landing/domains/content-card/style.scss
 44:2  ✖  Unexpected unknown type selector                 selector-type-no-unknown
          "content-card__alternate-action-button"

[brookewp]

Thanks for sharing, @manzoorwanijk! I'm not sure why they aren't showing up when I run yarn lint:css but I'll fix those two as well.