Changed every `docs` variant into `doc` as decided in #2663 (#6412)

var/spack/repos/builtin/packages/flux/package.py

var/spack/repos/builtin/packages/py-brian2/package.py

var/spack/repos/builtin/packages/py-elephant/package.py

var/spack/repos/builtin/packages/py-pythonqwt/package.py

var/spack/repos/builtin/packages/py-qtconsole/package.py

var/spack/repos/builtin/packages/star-ccm-plus/package.py

var/spack/repos/builtin/packages/typhonio/package.py