Revalidate and close the dead-code sweep backlog item

Summary

REF-017 is now closed as a backlog-revalidation item rather than an active implementation item.

The meaningful live cleanup work from the original audit has already landed on current main:

• all remaining CCM_SETUNICODEFORMAT no-op calls were removed
• MAXCON5WIN9X was removed
• the stale WinNT note in TaskbarNotifier.cpp was removed

What still remains in the tree is intentionally out of scope for this item:

• deadlake PROXYSUPPORT attribution comments are being kept on purpose
• stdafx.h no longer matches the older stale audit wording and does not carry a concrete dead-guard change that should be forced through this item

Revalidation Result

Current main no longer has the original broad dead-code workload that justified keeping this item open:

• no CCM_SETUNICODEFORMAT hits remain in srchybrid
• no MAXCON5WIN9X references remain
• no #if 0 hits remain in srchybrid
• no _MSC_VER < 1400 guards remain in stdafx.h
• the only remaining targeted hits from the original audit are the intentional deadlake PROXYSUPPORT comments

Because those comments are now explicitly accepted, there is no remaining implementation work for REF-017.

Final Disposition

• Marked Done
• No further code change required
• Any future proxy-comment cleanup would be a separate readability-only choice, not unfinished REF-017 work

Acceptance

• [x] Original live dead-code sub-work was revalidated against current main
• [x] Earlier landed cleanup is reflected in the item status
• [x] Remaining deadlake PROXYSUPPORT comments are intentionally accepted
• [x] REF-017 no longer blocks on stale audit wording