Eliminate amphtml link relation from AMP-to-AMP linking

[bartoszgadomski]

Summary

Fixes #6599

The amphtml link relation is no longer added since it has served no purpose. Additionally, the noamphtml relation is no longer added to the mobile version switcher link.

Checklist

• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Plugin builds for d49b860 are ready 🛎️!

• Download development build
• Download production build

[westonruter]

I think this may be too conservative in its exclusion, by limiting it to only WebPage, which is just one subtype of CreativeWork. There are many others, like AboutPage or AmpStory. These also fail if there is a rel attribute present. So I think the check should rather be for whether there is a property attribute on the link, and if so, skip adding the rel.

Or given that the amphtml link relation has served no purpose since we introduced it, we should just eliminate adding it altogether.

[bartoszgadomski]

Thanks @westonruter for your comment. What about the rel=noamphtml, does this have any purpose or can be removed as well?

[westonruter]

What about the rel=noamphtml, does this have any purpose or can be removed as well?

Adding it doesn't really have a purpose, no. As a page author you can disable AMP-to-AMP linking for an individual link if you give it the noamphtml relation. But otherwise, there's not any known need to add the relation when AMP-to-AMP is being excluded

[milindmore22]

Works as expected

[codecov]

Codecov Report

Merging #6661 (f1627b6) into develop (0478c24) will increase coverage by 1.20%.
The diff coverage is 100.00%.

❗ Current head f1627b6 differs from pull request most recent head d49b860. Consider uploading reports for the commit d49b860 to get more accurate results

@@              Coverage Diff              @@
##             develop    #6661      +/-   ##
=============================================
+ Coverage      76.38%   77.58%   +1.20%     
- Complexity      6475     6476       +1     
=============================================
  Files            261      198      -63     
  Lines          20697    19519    -1178     
=============================================
- Hits           15809    15144     -665     
+ Misses          4888     4375     -513     

Flag	Coverage Δ
javascript	?
php	77.58% <100.00%> (+0.06%)	⬆️
unit	77.58% <100.00%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
includes/sanitizers/class-amp-link-sanitizer.php	85.71% <100.00%> (+13.54%)	⬆️
src/MobileRedirection.php	83.51% <100.00%> (ø)
...src/components/site-scan-context-provider/index.js
...block-validation/components/error/error-content.js
assets/src/components/clipboard-button/index.js
assets/src/components/svg/check.js
assets/src/components/svg/standard.js
assets/src/block-editor/store/selectors.js
assets/src/components/amp-drawer/index.js
...mponents/use-template-mode-recommendation/index.js
... and 56 more