Utilities/Release: Remove unused documentation build settings

Since commit 37e015d4a6 (Utilities/Sphinx: Refactor Sphinx reference
recording, 2023-03-08, v3.27.0-rc1~342^2~1) our documentation requires
Python 3.7 or higher.  This is not available in the base images we use
to build Linux release binaries.  These days our release packaging CI
pipeline builds the documentation in a separate job anyway.

.gitlab/os-linux.yml

@@ -509,8 +509,7 @@
         - source .gitlab/ci/env.sh
         # Bootstrap.
         - mkdir -p build/
-        # Exclude documentation.  A job dependency provides it for packaging.
-        - sed '/^# Build doc/,/^$/d' Utilities/Release/linux/$CMAKE_ARCH/cache.txt > build/CMakeCache.txt
+        - cp Utilities/Release/linux/$CMAKE_ARCH/cache.txt build/CMakeCache.txt
         # Make sccache available.
         - .gitlab/ci/sccache.sh
         - export PATH=$PWD/.gitlab:$PATH

Utilities/Release/linux/aarch64/cache.txt

@@ -24,13 +24,6 @@ CMake_GUI_DISTRIBUTE_WITH_Qt_LGPL:STRING=3
 CMAKE_PREFIX_PATH:STRING=/opt/qt
 CMake_QT_STATIC_QXcbIntegrationPlugin_LIBRARIES:STRING=/opt/qt/plugins/platforms/libqxcb.a;/opt/qt/lib/libQt5XcbQpa.a;/opt/qt/lib/libQt5ServiceSupport.a;/opt/qt/lib/libQt5EdidSupport.a;/opt/qt/lib/libQt5EventDispatcherSupport.a;/opt/qt/lib/libQt5FontDatabaseSupport.a;/opt/qt/lib/libQt5ThemeSupport.a;/opt/qt/lib/libxcb-static.a;-lxcb;-lfontconfig;-lfreetype
 
-# Build documentation.
-SPHINX_EXECUTABLE:FILEPATH=/usr/local/bin/sphinx-build
-SPHINX_HTML:BOOL=ON
-SPHINX_MAN:BOOL=ON
-SPHINX_QTHELP:BOOL=ON
-QHELPGENERATOR_EXECUTABLE:PATH=/opt/qt/bin/qhelpgenerator
-
 # We bootstrap as part of the build so skip its test.
 CMake_TEST_BOOTSTRAP:BOOL=FALSE
 

Utilities/Release/linux/x86_64/cache.txt

@@ -24,13 +24,6 @@ CMake_GUI_DISTRIBUTE_WITH_Qt_LGPL:STRING=3
 CMAKE_PREFIX_PATH:STRING=/opt/qt
 CMake_QT_STATIC_QXcbIntegrationPlugin_LIBRARIES:STRING=/opt/qt/plugins/platforms/libqxcb.a;/opt/qt/lib/libQt5XcbQpa.a;/opt/qt/lib/libQt5ServiceSupport.a;/opt/qt/lib/libQt5EdidSupport.a;/opt/qt/lib/libQt5EventDispatcherSupport.a;/opt/qt/lib/libQt5FontDatabaseSupport.a;/opt/qt/lib/libQt5ThemeSupport.a;/opt/qt/lib/libxcb-static.a;-lxcb;-lfontconfig;-lfreetype
 
-# Build documentation.
-SPHINX_EXECUTABLE:FILEPATH=/opt/rh/rh-python36/root/usr/bin/sphinx-build
-SPHINX_HTML:BOOL=ON
-SPHINX_MAN:BOOL=ON
-SPHINX_QTHELP:BOOL=ON
-QHELPGENERATOR_EXECUTABLE:PATH=/opt/qt/bin/qhelpgenerator
-
 # We bootstrap as part of the build so skip its test.
 CMake_TEST_BOOTSTRAP:BOOL=FALSE