Remove `Object` and `RawObject` types from `pkg/core/object` package.
Use `Object` type from NeoFS SDK Go library everywhere. Avoid using the
deprecated elements.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
This function already reused in different storage engine parts
so it makes sense to keep it in separate package.
Signed-off-by: Alex Vanin <alexey@nspcc.ru>
