Remove fj::Sweep::color

It's not necessary, as it's just an alias for a method that is almost as
easy to access. And it's confusing, as it implies that a sweep has its
own color that's potentially separate from the swept shape.

fj-operations/src/sweep.rs

@@ -10,7 +10,7 @@ impl ToShape for fj::Sweep {
             self.shape().to_shape(tolerance, debug_info),
             Vector::from([0., 0., self.length()]),
             tolerance,
-            self.color(),
+            self.shape().color(),
         )
     }
 

fj/src/shape_3d.rs

@@ -113,11 +113,6 @@ impl Sweep {
     pub fn length(&self) -> f64 {
         self.length
     }
-
-    /// Access the color of the shape being swept
-    pub fn color(&self) -> [u8; 4] {
-        self.shape().color()
-    }
 }
 
 impl From<Sweep> for Shape {