removeField method
Removes from /Fields the entry that points to reference.
Looks in the root first and then descends through /Kids. An intermediate
node left without children is removed along with it: a field with no
widget and no /Kids is no longer reachable by the reader, and leaving it
pointing to nothing is exactly the inconsistency item D3 of the roadmap
describes.
Returns true when some entry was taken out.
Implementation
bool removeField(PdfIndirect reference) {
final fields = writableFields();
if (fields == null) return false;
return _removeFromFieldList(fields, reference, 0);
}