Wraps FPDFAnnot_RemoveObject. The object is identified by its
position within the annotation's embedded content (one-based,
matching pdf_annot_objects()). PDFium destroys the object and
regenerates the annotation's appearance stream. The handles to the
object from earlier pdf_annot_objects() calls on annot are
closed, and so are the clip paths and nested objects read from
them: further calls on them error cleanly. The handles to the
remaining objects stay valid, but their positions shift down by
one; call pdf_annot_objects() again for the new positions.
Objects read through another handle to the same annotation, for
example from a second pdf_annotations() call, are separate copies
and are not affected.