dev: Default building with Qt6 on all platforms (#5716)

.CI/full-ubuntu-build.sh

@@ -29,7 +29,6 @@ cmake \
     -DCMAKE_EXPORT_COMPILE_COMMANDS=On \
     -DCHATTERINO_PLUGINS="$C2_PLUGINS" \
     -DCMAKE_PREFIX_PATH="$Qt6_DIR/lib/cmake" \
-    -DBUILD_WITH_QT6="$C2_BUILD_WITH_QT6" \
     -DCHATTERINO_STATIC_QT_BUILD=On \
     -DCMAKE_CXX_FLAGS="-fno-sized-deallocation" \
     .

.CI/setup-clang-tidy.sh

@@ -19,7 +19,6 @@ cmake -S. -Bbuild-clang-tidy \
     -DCMAKE_EXPORT_COMPILE_COMMANDS=On \
     -DCHATTERINO_LTO=Off \
     -DCHATTERINO_PLUGINS=On \
-    -DBUILD_WITH_QT6=On \
     -DBUILD_TESTS=On \
     -DBUILD_BENCHMARKS=On