Revert "Revert "Revert "Uses a better cleaning command, closes #2203"""

This reverts commit 4e7d40e.

Actually it is the cause of JS removal

Author: zoffixznet

util/update-and-sync

@@ -30,10 +30,7 @@ echo 'Cleaning out old HTML files'
 # don't clean out html/ entirely, because there are some files
 # under version control there
 # build-log has been moved elsewhere, however
-# find html/ -name '*.html' -delete # This was the former order
-# This new one will clean all files not under source control.
-# Use only in the machine where you are going to run things.
-git clean -fd
+find html/ -name '*.html' -delete
 
 # if the htmlify fails, sync the build log.
 # since sync-build-log returns false, not the whole thing is synced