fix(corpus): drop 5 redundant scenarios — PR-3 covers these BIPIA rows

After merging PR-3 (#213, BIPIA corpus expansion across 5 tasks) into
main, the 5 corpus YAMLs that PR-2 bundled as a datamarking test bed
are now redundant:

- bipia-bipia-attack-email-00000-013.yaml — PR-3 imported row 00000 as 011
- bipia-bipia-attack-email-00001-014.yaml — PR-3 imported row 00001 as 012
- bipia-bipia-attack-email-00002-015.yaml — PR-3 imported row 00002 as 013
- is-060-pr2-authored-summarization-001-011.yaml — PR-3 synthesised 7 summarisation scenarios (#99001–99007)
- is-060-pr2-authored-summarization-002-012.yaml — same as above

PR-3's coverage is more diverse (9 email + 7 table + 3 code + 7 web +
7 summarisation, 33 total) and authoritative as the project's BIPIA
corpus. PR-2's value is the datamarking transform + tests + metrics
+ config. The transform doesn't depend on these YAMLs existing —
the new corpus from PR-3 is the measurement bed.

Validator: 91/91 scenarios valid (58 prior + 33 from PR-3).

Author: epappas