Follow job rename in openstack-manuals, remove now unused
checkbuild environment and simplify build-index.sh script
since the same content is build everytime.
Also remove www/www-index.html, we do not use it anymore.
Depends-On: https://review.opendev.org/676956
Change-Id: I00b5afc14fc7872edc1c9db9a0aaa7949b1f1443
b04c695b2c