fix(swingset): test-marshal.js: delete leftover+slow kernel creation

For some reason, most of the deserialization tests in test-marshal.js have
been creating a full SwingSet controller and then throwing it away. This is
an ancient leftover from the PlaygroundVat days, and removing it reduces the
test's runtime from about 20 seconds to just 1.

packages/SwingSet/test/test-marshal.js

@@ -9,8 +9,6 @@ import { WeakRef, FinalizationRegistry } from '../src/weakref.js';
 import { makeDummyMeterControl } from '../src/kernel/dummyMeterControl.js';
 import { makeMarshaller } from '../src/kernel/liveSlots.js';
 
-import { buildVatController } from '../src/index.js';
-
 const gcTools = harden({
   WeakRef,
   FinalizationRegistry,
@@ -23,12 +21,6 @@ function makeUnmeteredMarshaller(syscall) {
   return { m, unmeteredUnserialize };
 }
 
-async function prep() {
-  const config = {};
-  const controller = await buildVatController(config);
-  await controller.run();
-}
-
 test('serialize exports', t => {
   const { m } = makeMarshaller(undefined, gcTools);
   const ser = m.serialize;
@@ -56,7 +48,6 @@ test('serialize exports', t => {
 });
 
 test('deserialize imports', async t => {
-  await prep();
   const { unmeteredUnserialize } = makeUnmeteredMarshaller(undefined);
   const a = unmeteredUnserialize({
     body: '{"@qclass":"slot","index":0}',
@@ -93,7 +84,6 @@ test('deserialize exports', t => {
 });
 
 test('serialize imports', async t => {
-  await prep();
   const { m, unmeteredUnserialize } = makeUnmeteredMarshaller(undefined);
   const a = unmeteredUnserialize({
     body: '{"@qclass":"slot","index":0}',
@@ -144,7 +134,6 @@ test('serialize promise', async t => {
 });
 
 test('unserialize promise', async t => {
-  await prep();
   const log = [];
   const syscall = {
     subscribe(promiseID) {