Remove ambiguous text_color attributes for Checkbox and Radio

Instead, always use a `StyleSheet`.

examples/scrollable/src/style.rs

@@ -116,6 +116,7 @@ mod dark {
                 dot_color: ACTIVE,
                 border_width: 1.0,
                 border_color: ACTIVE,
+                text_color: None,
             }
         }
 

examples/styling/src/main.rs

@@ -343,6 +343,7 @@ mod style {
                     dot_color: ACTIVE,
                     border_width: 1.0,
                     border_color: ACTIVE,
+                    text_color: None,
                 }
             }
 
@@ -528,10 +529,10 @@ mod style {
                     background: if is_checked { ACTIVE } else { SURFACE }
                         .into(),
                     checkmark_color: Color::WHITE,
-                    text_color: Color::BLACK,
                     border_radius: 2.0,
                     border_width: 1.0,
                     border_color: ACTIVE,
+                    text_color: None,
                 }
             }