Switch to faster thresholding code

The hand-unrolled version wasn't actually faster. The
compiler-unrollable version from before actually is though. It's also
much shorter.

Change-Id: I450c4f7ae12e25e06da0b60a308eaeaea4cb05d7
diff --git a/y2019/vision/target_sender.cc b/y2019/vision/target_sender.cc
index 3a6fbfe..6d868f8 100644
--- a/y2019/vision/target_sender.cc
+++ b/y2019/vision/target_sender.cc
@@ -95,7 +95,7 @@
                             monotonic_clock::time_point monotonic_now) {
     aos::vision::ImageFormat fmt{640, 480};
     aos::vision::BlobList imgs = aos::vision::FindBlobs(
-        aos::vision::SlowYuyvYThreshold(fmt, data.data(), 120));
+        aos::vision::FastYuyvYThreshold(fmt, data.data(), 120));
     finder_.PreFilter(&imgs);
     LOG(INFO, "Blobs: (%zu).\n", imgs.size());