COMP: Drop the DCMTK `offile.h` printf-format overlay once DCMTK/dcmtk#151 merges

[hjmjohnson]

ITK's DCMTK fork branch carries a local overlay commit adding printf format
attributes to OFFile's printf wrappers. It was submitted upstream as
DCMTK/dcmtk#151, which is still open.
When it merges, the overlay should be dropped at the next DCMTK bump.

Current pin and overlay state

Modules/ThirdParty/DCMTK/DCMTKGitTag.cmake:46:

set(DCMTK_GIT_TAG "554b74475ba1734655c61988b94bc69daf6690c7") # for/itk-dcmtk-3.7.0-ccfd10b

DCMTK is fetched (not vendored) — Modules/ThirdParty/DCMTK/CMakeLists.txt:144-145
uses GIT_REPOSITORY ${DCMTK_GIT_REPOSITORY} / GIT_TAG ${DCMTK_GIT_TAG} — so
the overlay lives on the InsightSoftwareConsortium/DCMTK branch
for/itk-dcmtk-3.7.0-ccfd10b, of which 554b7447 is the tip.

The overlay is commit 84c8047db: it adds
__attribute__((format(printf, ...))) to OFFile::fprintf / OFFile::vfprintf
in ofstd/include/dcmtk/ofstd/offile.h, silencing two clang
-Wformat-nonliteral warnings that otherwise appear in every translation
unit that includes offile.h.

Upstream status and retirement steps

DCMTK/dcmtk#151 — Add printf format attribute to OFFile printf wrappers —
state OPEN, mergedAt: null, last updated 2026-07-14.

When it merges:

1. Rebase for/itk-dcmtk-3.7.0-ccfd10b onto the upstream commit containing the
   merged change.
2. Drop 84c8047db from the overlay.
3. Bump DCMTK_GIT_TAG in Modules/ThirdParty/DCMTK/DCMTKGitTag.cmake.
4. Update the local-patch list in Modules/ThirdParty/DCMTK/README.md.

Should be folded into the next routine DCMTK version bump rather than done as a
standalone change.

Prior ITK history

ITK PR #6587 attempted to carry this and was closed unmerged — #6548
("COMP: Pin DCMTK with single-export namespace fix", merged 2026-07-14) had
already advanced the pin past the commit #6587 targeted. So no ITK PR or issue
currently records the retire-on-upstream-merge condition; hence this tracking
issue.

Same shape as #6694 (re-vendor MetaIO, blocked on Kitware/MetaIO#145).