Change: Remove color tooling from build chain

We've decided to remove color tooling from the build chain of the design system. Previously it was possible to
- define color contrast rules for the tokens in the colors.yaml file
- define transformations on colors in the colors.yaml file (e.g. lighten, darken, ...)
Since the dependencies we used are not well maintained and designers most likely bring their own tools, we've
decided that the colors.yaml file is supposed to only contain the resulting color values, not any transformations
or rules anymore.

https://github.com/owncloud/web/pull/10264
