RFR: 8343071: Broken anchors to restricted method page and some redundant ids

[Nizar Benalla]

Can I get a review for this patch that brings the last changes to fix broken anchors in the source code.

The links updated in this patch can be grouped into 3 sections, they were minor so I grouped them into one PR.

1- Move some references from the old `foreign/package-summary.html#restricted` to the new `Restricted Methods` page, these were broken after https://github.com/openjdk/jdk/commit/f4dccfd4cf354f360b823c8cce15bb54ef90e9ca

2- Remove a redundant `<a>` tag in `Class.java`, the id not needed as we already created an index.

3- Fix some broken anchors in `StructuredTaskScope.java`, the text will be updated in a JEP but we can fix the current text now. 

Thanks!

-------------

Commit messages:
 - fix various links

Changes: https://git.openjdk.org/jdk/pull/21839/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21839&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343071
  Stats: 7 lines in 4 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/21839.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21839/head:pull/21839

PR: https://git.openjdk.org/jdk/pull/21839