Add impl_url for removed X-XSS-Protection header

[bsmth]

Summary

Adding impl_ulrs for some HTTP features. These were documented in MDN content prose, and removed in recent PRs.

• https://github.com/mdn/content/pull/36862/files#diff-35a3c4188ae51e9b163064c8122d7916123841263089a1f06d74b0a554b731cf

Related issues

Follow-up from:

• chore(http): Refresh headers ~[s->x] content#36862

[caugner]

@queengooborg Would you know why the linter complains, although this PR only adds impl_urls?

Testing all features together...
 ✖ Obsolete - Unnecessary exception → http.headers.X-XSS-Protection

[queengooborg]

Oh! That's because we had an exception to the obsolete features linter for this feature, but now that an implementation URL is being added, the feature is no longer considered obsolete and the exception can be removed!

[bsmth]

Thank you, both!