Document withdrawal of dcrypt 2.0.0

[NoCentralHub]

Summary

dcrypt 2.0.0 has been withdrawn and yanked because it violates the project's
zero-unsafe, zero-native-code, and zero-FFI implementation policy. Version
1.2.3 has also been yanked and is not a safe fallback. No maintainer-supported
patched release is currently available.

This follow-up:

• adds a prominent withdrawal warning to all four dcrypt advisories;
• replaces the deleted-release reference with the durable upstream withdrawal
  notice; and
• removes recommendations to deploy 2.0.0 while preserving the technically
  accurate vulnerability ranges and patched >= 2.0.0 metadata for these four
  specific flaws.

The withdrawal is a separate implementation-policy correction. It does not
assert that these four named vulnerabilities persist in 2.0.0, and the
immutable v2.0.0 tag remains available as historical provenance.

Upstream notice:
https://github.com/ioi-foundation/dcrypt/blob/master/docs/security/V2.0.0-WITHDRAWAL.md

Validation

• rustsec-admin lint
• git diff --check

[djc]

Needs a rebase after ID assignment.

Please avoid relying more on advisory-db review until you're more certain all the issues have been resolved.

(Personally I would suggest using graviola instead of reimplementing all this crypto stuff.)