Clean up DomainMapper_Impl::PushShapeContext()

It doesn't make sense to set anchor type here: either the VML import
already set it, or it should be set when the anchor/inline token
arrives.

Additionally, this basically ensured that non-inline pictures are either
inline or at-page anchored, and both of those values are incorrect.

Change-Id: Ic71aeca9da333665a2749bb0aabbb9b63cee0c00
DOCX OLE import: inherit anchor type from replacement graphic

Change-Id: Ic8b6f423acae5cc7e3799cf20e672b56a9cc8c0c