v4.0: blockstore: mark CMR conflicts as dead under validate_chained_block_id (backport of #11334)

[mergify]

Problem

The feature chained_merkle_conflict_duplicate_proofs was designed pre enforce_fixed_fec_set in order to notice duplicate blocks when there were undersized FEC sets.

With enforce_fixed_fec_set this feature is no longer needed and has been abandoned.

However FD requires that the CMR is correct across FEC sets. We do not need to mark the block as duplicate or send some sort of duplicate proofs via gossip, just mark the block as dead.

Summary of Changes

As part of SIMD-0340, mark the block as dead instead. In a follow up we'll remove the abandoned feature.
We wish to backport this PR as SIMD-0340 is critical for FD and needs to be activated in 4.0

See the amendment
solana-foundation/solana-improvement-documents#502

---

This is an automatic backport of pull request #11334 done by Mergify.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.0%. Comparing base (ca034bd) to head (40640d0).

Additional details and impacted files

@@            Coverage Diff            @@
##             v4.0   #11558     +/-   ##
=========================================
- Coverage    83.0%    83.0%   -0.1%     
=========================================
  Files         838      838             
  Lines      316793   316786      -7     
=========================================
- Hits       263229   263190     -39     
- Misses      53564    53596     +32     

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