Change wording in Night Light KCM to reflect scientific consensus

Until there's conclusive science that color temperature affects eye strain,
KDE should not make any such claims.

There is no scientific evidence that blue light from computer monitors has
anything to do with eye strain or sleep patterns. This is folklore based on
some faulty research from decades ago that somehow made it into the mainstream.

Color temperature ends up being just a matter of personal preference. Actual
studies  using lenses showed that blocking blue light did not help people who
suffer from eye strain at all (a TL;DR of many studies is this:
https://pubmed.ncbi.nlm.nih.gov/29044670/).

Some other links, digested for popular science:
- https://onezero.medium.com/blue-light-isnt-as-bad-as-you-think-d9e1e48f0cc6
- https://time.com/5752454/blue-light-sleep/