Remove discussion of "invalid Atom".
APP draft-06 is overspecified; it makes MAY-level requirements about Atom content that doesn't meet MUST-level requirements of AtomFormat. The text up for deletion does not enhance interoperability, and was inserted without consulting the working group.
remove from "8.1 Creating resources with POST",
Clients MAY POST invalid Atom for initial resource creation - specifically the id and link elements MAY be omitted.