Do not attempt to install cmake a second time when building macOS or Linux wheels

[radarhere]

#8497 added

Pillow/.github/workflows/wheels-dependencies.sh

Lines 185 to 186 in d7ffb39

	# Ensure cmake is available
	python3 -m pip install cmake

to the macOS and Linux wheels.

However, we still have an alternative attempt to install cmake.

Pillow/.github/workflows/wheels-dependencies.sh

Lines 77 to 82 in d7ffb39

	function build_brotli {
	if [ -e brotli-stamp ]; then return; fi
	local cmake=$(get_modern_cmake)
	local out_dir=$(fetch_unpack https://github.com/google/brotli/archive/v$BROTLI_VERSION.tar.gz brotli-$BROTLI_VERSION.tar.gz)
	(cd $out_dir \
	&& $cmake -DCMAKE_INSTALL_PREFIX=$BUILD_PREFIX -DCMAKE_INSTALL_LIBDIR=$BUILD_PREFIX/lib -DCMAKE_INSTALL_NAME_DIR=$BUILD_PREFIX/lib . \

where get_modern_cmake is from multibuild.

That can now be removed.