Charts: Deprecate themeVariant prop for light / dark themes #7369
Description
The charts have a themeVariant property, which was intended for light and dark themes. However, PatternFly's dark theme will be enabled by adding class="pf-theme-dark" to the <html> element.
Since the chart variables will automatically pick up this change, there is no need for themeVariant and it should be deprecated.
Note: themeVariant was never supported, it always defaulted to the light theme.