Navigation: Remove unnecessary __experimentalStyle

[t-hamano]

Closes #59142
Rleated to #51710, #52579

What?

This PR removes unnecessary __experimentalStyle from the Navigation menu.

Why?

From what I've researched, this is an accidental regression caused by the timing of two PRs being merged.

Below are the PRs related to this issue and the dates and times they were merged.

• Nav block: link text color inheritance fixes and tests #51710
  • Merged date: Jul 13, 2023, 11:23 PM GMT+9
  • __experimentalStyle has been removed to the block.json (Source)
• Add filter to turn off Interactivity API for a block #52579
  • Merged date: Jul 14, 2023, 2:36 AM GMT+9
  • __experimentalStyle has been re-added to the block.json. (Source)

As you can see, the times when the two PRs were merged are very close. Perhaps the latter PR did not include the former PR, so __experimentalStyle was added unintentionally.

Testing Instructions

Since the stylesheet already exists, there will be no side effects of deleting it. As shown below, color: inherit; should still be applied to links in the navigation block.

trunk	This PR

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[MaggieCabrera]

Yeah, that looks correct to me. I believe we should have this covered with e2e tests too

[t-hamano]

@MaggieCabrera Thanks for the review!

I believe we should have this covered with e2e tests too

Isn't the default color tested here? This PR only removes duplicate color:inherit, so it might be difficult to verify this with E2E tests.

[t-hamano]

For now, I would like to merge this PR. If we need additional e2e testis, I'd be happy to do that as a follow-up.