This was a small part of the Material Theme System Updates project.

As of Flutter 1.17, the ThemeData accent properties - accentColor,
accentColorBrightness, accentIconTheme, and accentTextTheme - were no
longer used by the Material library. They had been replaced by
dependencies on the theme’s colorScheme and textTheme properties as
part of the long-term goal of making the default configurations of the
material components depend almost exclusively on these two
properties.

The motivation for these changes is to make the theme system easier to
understand and use. The default colors for all components are to be
defined by the components themselves and based on the color
scheme. The defaults for specific component types can be overridden
with component-specific themes like FloatingActionButtonThemeData or
CheckBoxTheme. Previously, properties like accentColor were used by a
handful of component types and only in some situations, which made it
difficult to understand the implications of overriding them.

Description of change