remove mentions to legacy tags from official extension docs as legacy versions are deprecated

[aalves08]

Summary

Fixes #13757

Occurred changes and/or fixed issues

• remove mentions to legacy tags from official extension docs as legacy versions are deprecated

Technical notes summary

Areas or cases that should be tested

Areas which could experience regressions

Screenshot/Video

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes
• The PR has been reviewed in terms of Accessibility
• The PR has considered, and if applicable tested with, the three Global Roles Admin, Standard User and User Base

[rak-phillip]

LGTM