macpython: Do not install ninja again in module builds

Ninja is already installed and made available in the 2.7 venv earlier in the
script. This works around an installation error that occurs wiht Python 3.6.

Author: thewtex

scripts/macpython-build-module-wheels.sh

@@ -45,8 +45,6 @@ for VENV in "${VENVS[@]}"; do
     if [[ -e $PWD/requirements-dev.txt ]]; then
       ${PYTHON_EXECUTABLE} -m pip install --upgrade -r $PWD/requirements-dev.txt
     fi
-    ${PYTHON_EXECUTABLE} -m pip install --no-cache ninja
-    NINJA_EXECUTABLE=${VENV}/bin/ninja
     itk_build_path="${SCRIPT_DIR}/../ITK-${py_mm}-macosx_x86_64"
     ${PYTHON_EXECUTABLE} setup.py bdist_wheel --build-type MinSizeRel --plat-name macosx-10.9-x86_64 -G Ninja -- \
       -DCMAKE_MAKE_PROGRAM:FILEPATH=${NINJA_EXECUTABLE} \