Bug 1610512 - Part 5: Updating ICU requires a clobber. r=jwalden

Depends on D66558

Differential Revision: https://phabricator.services.mozilla.com/D66559

--HG--
extra : moz-landing-system : lando

CLOBBER

@@ -22,4 +22,4 @@
 # changes to stick? As of bug 928195, this shouldn't be necessary! Please
 # don't change CLOBBER for WebIDL changes any more.
 
-Merge day clobber
+Bug 1610512 - Update to ICU 66 requires clobber