Remove private methods with single call site
Remove private methods with single call site

- LazyBlobDock.__remove_cached_attachment
- LazyBlobDock.__store_lazy_attachment
dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq