CI: Fix and simplify glob for baseline screenshot

...for evergreen browsers

Whoops previous commit was broken because the double quotes were
preventing the glob from expanding. So fix that but also I discovered
that we don't need the `ls` or the `sh -c` if we don't do the double
quotes, just having another layer of subshell (the `$(...)`) will expand
the glob.

circle.yml

diff --git a/circle.yml b/circle.yml
index e68e1fc..7ee2fa4 100644
--- a/circle.yml
+++ b/circle.yml
@@ -212,7 +212,7 @@
       for file in $(ls *.png); do
         # if evergreen browser, browser version of previous screenshot may not match,
         # so replace previous browser version with glob
-        baseline="$(sh -c "ls \"baseline/$(echo $file | sed 's/[^_]*_(evergreen)/*/')\"")"
+        baseline="$(echo baseline/$(echo $file | sed 's/[^_]*_(evergreen)/*/')"
         echo "Number of different pixels from baseline in $file:"
         compare -metric AE $baseline $file ${file/%.png/_DIFF.png}
       done