COMP: Remove broken duplicate-declaration sed hack from doc CI

The "Remove Duplicate Declaration Warnings" step deleted line 6559 of
Sphinx's domains/cpp.py, but in the pinned sphinx==7.2.6 that line is an
unrelated template-parsing heuristic, not the duplicate-declaration
warning (emitted elsewhere). The step therefore mutated an unrelated
code path while suppressing nothing, and it relied on distutils, which
is removed in Python 3.12.

Drop the step and instead declare the intent in Sphinx configuration via
suppress_warnings = ['duplicate_declaration.cpp']. The same ITK class is
deliberately documented by multiple examples, so the duplicate is
expected. The key is ignored by sphinx==7.2.6 and becomes effective once
Sphinx is upgraded, after which the CTest warning exception can also be
dropped.

Author: hjmjohnson

.github/workflows/build-test-publish.yml

@@ -319,11 +319,6 @@ jobs:
 
           echo "Workspace: ${{ github.workspace }}"
 
-      - name: Remove Duplicate Declaration Warnings
-        run: |
-          SITE_PACKAGES_DIR=$(python3 "-c" "from distutils import sysconfig; print(sysconfig.get_python_lib())")
-          sed -i "6559d" ${SITE_PACKAGES_DIR}/sphinx/domains/cpp.py
-
       - name: Restore ExternalData cache
         uses: actions/cache@v4
         with:

Formatting/conf.py.in

@@ -45,6 +45,11 @@ if os.environ.get("READTHEDOCS", "") == "True":
 # C++ is the primary (default) Sphinx domain.
 primary_domain = 'cpp'
 
+# The same ITK class is intentionally documented by more than one example,
+# so the C++ domain reports duplicate declarations. Suppress that subtype
+# (effective on Sphinx versions that tag the warning).
+suppress_warnings = ['duplicate_declaration.cpp']
+
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = ['sphinx.ext.todo', 'sphinx.ext.imgmath', 'sphinx.ext.ifconfig',