Some more flatten-tree aliases

Some more flatten-tree aliases

* lisp/allout.el (allout-flatten):
* lisp/progmodes/hideif.el (hif-flatten):
Now an obsolete alias for flatten-tree.  All callers changed.
* lisp/org/org-protocol.el (org-protocol-flatten):
Make it an alias for flatten-tree if available.
* lisp/progmodes/js.el (js--flatten-list):
Remove alias.  We shouldn’t need obsolete function aliases for
private functions.