Put all the thresholding code in the same place

This will make it easier to write tests validating the fast version.

Change-Id: I27cc372cc848c495d10a138b3c149d550dc0dad9
diff --git a/y2017/vision/target_finder.cc b/y2017/vision/target_finder.cc
index a6b049c..91e801e 100644
--- a/y2017/vision/target_finder.cc
+++ b/y2017/vision/target_finder.cc
@@ -103,17 +103,18 @@
 }
 
 aos::vision::RangeImage TargetFinder::Threshold(aos::vision::ImagePtr image) {
-  return aos::vision::DoThreshold(image, [&](aos::vision::PixelRef &px) {
-    if (px.g > 88) {
-      uint8_t min = std::min(px.b, px.r);
-      uint8_t max = std::max(px.b, px.r);
-      if (min >= px.g || max >= px.g) return false;
-      uint8_t a = px.g - min;
-      uint8_t b = px.g - max;
-      return (a > 10 && b > 10);
-    }
-    return false;
-  });
+  return aos::vision::ThresholdImageWithFunction(
+      image, [&](aos::vision::PixelRef px) {
+        if (px.g > 88) {
+          uint8_t min = std::min(px.b, px.r);
+          uint8_t max = std::max(px.b, px.r);
+          if (min >= px.g || max >= px.g) return false;
+          uint8_t a = px.g - min;
+          uint8_t b = px.g - max;
+          return (a > 10 && b > 10);
+        }
+        return false;
+      });
 }
 
 void TargetFinder::PreFilter(BlobList &imgs) {