VOM: remove linkToCohort/unweakable for KindHandle prototypes

Now that `kindHandleToID` is a *strong* Map, KindHandles are held
strongly, from definition/reanimation time through to the end of the
incarnation. That means their prototype is no longer useful as a GC
sensor, and we don't need to use `linkToCohort` or `unweakable` to
prevent userspace from trying.

packages/swingset-liveslots/src/virtualObjectManager.js

@@ -1049,8 +1049,6 @@ export function makeVirtualObjectManager(
     // eslint-disable-next-line @typescript-eslint/prefer-ts-expect-error -- https://github.com/Agoric/agoric-sdk/issues/4620
     // @ts-ignore cast
     const kindHandle = Far('kind', {});
-    linkToCohort.set(Object.getPrototypeOf(kindHandle), kindHandle);
-    unweakable.add(Object.getPrototypeOf(kindHandle));
     kindHandleToID.set(kindHandle, kindID);
     kindIDToDescriptor.set(kindID, durableKindDescriptor);
     registerValue(kindIDvref, kindHandle, false);