CI: Skip raw diffs

Turns out the `-compose src` turns off the "shadow" of the image that
we're manually adding in on the next line:
https://www.imagemagick.org/Usage/compare/

Also, apparently `-list metric` will list every diff metric, that's
cool:
http://www.imagemagick.org/script/command-line-options.php?#metric

circle.yml

diff --git a/circle.yml b/circle.yml
index 5ba036c..8a0b308 100644
--- a/circle.yml
+++ b/circle.yml
@@ -197,7 +197,6 @@
                     | grep '\.png$' \
                     | grep -v '/pieces/' \
                     | grep -v '/baseline/' \
-                    | grep -v '/raw_diffs/' \
                     | sed "s:\$CIRCLE_ARTIFACTS/imgs/:-o $CIRCLE_ARTIFACTS/imgs/baseline/:")"
       echo 'Baseline image URLs and files:'
       echo
@@ -209,14 +208,12 @@
     # Generate image diffs.
     - |-
       cd $CIRCLE_ARTIFACTS/imgs/
-      mkdir raw_diffs/
       for file in $(ls *.png); do
         # if evergreen browser, browser version of previous screenshot may not match,
         # so replace previous browser version with glob
         baseline=baseline/"$(sh -c "ls $(echo $file | sed 's/[^_]*_(evergreen)/*/')")"
-        echo "Metric diff for $file:"
-        compare -metric AE -compose src $baseline $file raw_diffs/$file
-        composite -alpha on raw_diffs/$file $prev ${file/%.png/_DIFF.png}
+        echo "Diff metrics for $file:"
+        compare -list metric $baseline $file ${file/%.png/_DIFF.png}
       done
   post:
     - killall --wait sc; true  # wait for Sauce Connect to close the tunnel; ignore errors since it's just cleanup