cleanup and comment out unused functions

src/grid.rs

@@ -159,6 +159,8 @@ impl Grid {
         );
     }
 
+    // No longer needed (moved to imgdata.rs)
+    /*
     pub fn quantile(&self, fraction: f32) -> f32 {
         let index = if (fraction - 1.0_f32).abs() < f32::EPSILON {
             self.data.len() - 1
@@ -175,6 +177,7 @@ impl Grid {
     pub fn data(&self) -> &[f32] {
         &self.data
     }
+    */
 }
 
 pub fn combine<T>(grids: &mut [Grid], attraction_table: &[T])