Remove annotated-spec-related functionality from canvas tests (#26619)

* Remove more canvas annotated spec helpers

The functionality to generate an annotated canvas spec was removed in
commit dadd085, but remnants of it
have been lingering in the codebase, confusing anyone who tries to make
sense of the canvas tests. This removes those remnants.

* Remove 'previously' from canvas spec.yaml

This was used for disambiguation when generating an annotated spec that
is no longer generated.

* Remove <^> and <eol> from canvas spec.yaml

This is where links to the generated tests would be inserted in the
annotated spec, which is no longer generated.

Author: adroitwhiz