travis.ci is no longer used as a service

I also deleted files that had no content and
were not included in the docs.

Taken from oemof-solph commit 0b03a258fd6973ccd36bde9b4d1be285b87d81e7.

Flake8 also checks comments, but Black does not enforce this.
I would allow long comments for now.

This works around the problem that labels might be set inconsistently
because of multi-inheritence.

The CSP facade needs poa_horizontal_ratio, which is no longer available
in more recent versions of pvlib.

This is because Pyomo has no reproducible line order.

Following the renaming in solph.

Fix/setup

Solph >v0.5.5 requires numpy >= 2.0. However, the CSP facade needs
poa_horizontal_ratio, which is no longer available in pvlib >= 0.9.0.
And that legacy version of pvlib is not compatible to numpy >= 2.0.