clean up setup setting

[hamogu]

Now that CIAO uses matplotlib and allows astropy and other libraries in the same installation (through conda or in the traditional method), setting up things can be simplified. Just require that CIAO and astropy are available to run everything. That was, all conf.get('CIAO', 'setup') can be removed.

That not just to simplify the code (which saves only a few lines), but to make is conceptionally easier for other people to replicate this setup and run the tests.