Need to transfer relevant improvements from realms-shim into SES-shim.

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See Agoric/realms-shim#307

Agoric has stopped investing in the realms-shim. We participate in advancing the realms proposal, but our primary energy is in the compartment shim and proposals (and the related lockdown, harden, ...). Either we transfer it to some other stakeholder of the realms proposal (attn @caridy), or we should shut it down. However, we also need to ensure that any relevant improvements made to the realms shim (such as @ExE-Boss's Agoric/realms-shim#302) are also applied to the compartments / ses / lockdown shim (such as at https://github.com/Agoric/SES-shim/blob/master/packages/ses/src/repair-legacy-accessors.js)

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I think this issue is stale and can be shut down. @kriskowal @dckc @FUDCo @caridy please let me know if there's a reason to reopen it. Or just reopen it with the reason.