feat: clean up unused PaintFunction type

Author: mrkpatchaa

src/lib/icon-base.tsx

@@ -30,7 +30,7 @@ function IconBase({
     weight: contextWeight = 'regular',
     mirrored: contextMirrored = false,
     style: contextStyle,
-    duotoneColor: contextDuotoneColor = '#000',
+    duotoneColor: contextDuotoneColor,
     duotoneOpacity: contextDuotoneOpacity = 0.2,
   } = useContext(IconContext);
 

src/lib/index.tsx

@@ -9,8 +9,6 @@ export type IconWeight =
   | 'fill'
   | 'duotone';
 
-export type PaintFunction = (color: string) => React.ReactNode | null;
-
 export interface IconProps {
   color?: string;
   size?: string | number;