Remove manually defined anchors pointing to statement definitions

Remove manually defined anchors pointing to statement definitions

This is hopefully end of duplication. This batch did not cause clashes
in Sphinx but it was pointless nonetheless as we have auto-generated
anchors for all statements.

(cherry picked from commit 137e0f4e0e14975c7fc00000da2e77b5b29f61f5)

Adapted for v9_18 branch by doing cleanup also in
notes/notes-9.18.0.rst.