Do not require "Delete portal content" for copying.

Requiring "Delete portal content" was introduced accidentally for copying because of a patch for cutting.

Patch `OFS.CopySupport.cb_isCopyable` to no longer use the patched `cb_userHasCopyOrMovePermission`, which was patched to also require `Delete portal content` so that cutting works properly.

I decided to change `cb_isCopyable` rather than `cb_userHasCopyOrMovePermission` (and the cutting process) because I think it is safer to not introduce more problems with cutting.

@maethu @buchi can you take a look?
/cc @elioschmutz