graphics/vkd3d: strip non-debug builds

> Running Q/A tests (stage-qa)

Warning: 'lib/libvkd3d-utils.so.1.1.0' is not stripped consider trying INSTALL_TARGET=install-strip or using ${STRIP_CMD}
Warning: 'lib/libvkd3d-shader.so.1.0.0' is not stripped consider trying INSTALL_TARGET=install-strip or using ${STRIP_CMD}
Warning: 'lib/libvkd3d.so.1.2.0' is not stripped consider trying INSTALL_TARGET=install-strip or using ${STRIP_CMD}