How do I remove multiple owners from a file/folder? While trying to set up MAMP/PHPStorm, I CHOWNed the OWNER of my Sites folder to _www from myUser. Since this did not resolve the problem I was experiencing, I attempted to CHOWN myUser /Users/myUser/Documents/Sites... which worked, except Get Info shows both as owners, and ls -l reports _www as the (primary?) owner. I could not modify the folder contents, even though myUser is one of the owners.

When I ls -leO@ as suggested in this answer, I see the following:

drwxr-xr-x+ 31 _www  wheel  -  1054 Dec 5 12:38 Sites
  0: user:myUser allow list,add_file,search,add_subdirectory,delete_child,readattr,
  writeattr,readextattr,writeextattr,readsecurity


I sudo chown :staff Sites thinking this will give myUser more clout, and then sudo chown myUser: Sites which works in removing _www, but I'm left with:

MacBook-Pro:Documents myUser$ ls -leO@
...
drwxr-xr-x+ 31 myUser  staff  -  1054 Dec 5 12:38 Sites
  0: user:myUser allow list,add_file,search,add_subdirectory,delete_child,readattr,
  writeattr,readextattr,writeextattr,readsecurity
...


I've read the MAN page for CHMOD and ACL as suggested in this answer, and I've tried chmod -a#0 Sites and variations with no success. How do I remove the ACL/xattr?
I'm not sure how to do it from Terminal, but you could use a tool like BatChmod to redo the file permissions (and clear ACLs). 
http://www.lagentesoft.com/batchmod/