Comply with spec for permissions needed to delete a resource

Basically, until https://github.com/solid/web-access-control-spec/issues/47 gets discussed with a proper decision process, let's undo what was done in https://github.com/solid/node-solid-server/issues/729.

I'm not so fussed about the actual behaviour, I just want to start the process of documenting what we consider the spec (see also https://github.com/solid/solid-spec/issues/174), and on which points we are aware of differences between NSS and the spec.

Wherever such differences exist, if we think that NSS is right, then we should update the spec.
And if we think the spec is right (like in this case), we should (at least create a github issue to) fix NSS.

PS: If anyone is aware of any other points on which NSS is not spec-compliant, then let's create issues for each one of those. We can decide to willingly leave NSS broken, but at least we should have github issues that document how NSS is broken.

まず、リンクされている web-access-control-spec の issue 47、NSS の issue 729、solid-spec の issue 174 を読み、リソースを削除するための権限要件を比較します。issue にはファイルやテストの指定はありません。完了条件は、NSS と spec の違いを文書化して決定を記録することです。実装を変更する必要がある場合は、後続の NSS issue を作成します。