kcms/fonts: Remove warning about decimal font sizes
Reason for the change
This was a workaround for https://bugreports.qt.io/browse/QTBUG-92006, but that's been fixed for Plasma 6, hooray! So we don't need to irritate people about it anymore.
Test plan
Opened the KCM, set 10.01pt as the size for the General font. No warning anymore!
Bugs fixed
Closes #124 (closed)