remove xs:unit testing (#10207)

incidental

## Description
While working on #10202 I got a CI error that "no function" for the Zoe tests. It turned out to be that ava-xs doesn't support `t.snapshot`. So I added it to the voluminous "exclude" value and pushed again. Later I see CI [fails again](https://github.com/Agoric/agoric-sdk/actions/runs/11162498228/job/31027478876?pr=10202) because ava-xs is confused by the `snapshots` directory.

The `test:xs-unit` job is not carrying its weight. I can't recall it ever detecting an error that wasn't detected in Node. Maybe a while ago it did and it was an important line of defense. In the past year we've developed much more integration testing and I'm confident these tests are redundant. 

It generally doesn't hurt to test more, but ava-xs is so different from XS that the cost of reconciliation is too great.

### Security Considerations
none
### Scaling Considerations
none

### Documentation Considerations
none

### Testing Considerations
see above

### Upgrade Considerations
none

.github/workflows/test-all-packages.yml

@@ -609,6 +609,7 @@ jobs:
       - name: set vars
         id: vars
         # END-TEST-BOILERPLATE
+        # XXX test:xs-unit is deprecated branch protection still expects it
         run: |
           echo "node-version=${{ matrix.engine == 'xs' && '18.x' || matrix.engine }}" >> $GITHUB_OUTPUT
           echo "test=${{ matrix.engine == 'xs' && 'test:xs-unit' || 'test:unit' }}" >> $GITHUB_OUTPUT

packages/ERTP/package.json

@@ -13,8 +13,8 @@
     "postpack": "git clean -f '*.d.ts*' '*.tsbuildinfo'",
     "test": "ava",
     "test:c8": "c8 $C8_OPTIONS ava",
-    "test:xs": "yarn test:xs-unit && yarn test:xs-worker",
-    "test:xs-unit": "ava-xs",
+    "test:xs": "yarn test:xs-worker",
+    "test:xs-unit": "exit 0",
     "test:xs-worker": "SWINGSET_WORKER_TYPE=xs-worker ava -c 2 test/swingsetTests",
     "lint-fix": "yarn lint:eslint --fix",
     "lint": "run-s --continue-on-error lint:*",
@@ -64,15 +64,6 @@
     "exported.js",
     "exported.d.ts"
   ],
-  "ava-xs": {
-    "exclude": [
-      "swingsetTests",
-      "# fast-check unsupported",
-      "test/unitTests/amountProperties.test.js",
-      "test/unitTests/inputValidation.test.js",
-      "test/unitTests/issuerObj.test.js"
-    ]
-  },
   "ava": {
     "files": [
       "test/**/*.test.*"

packages/zoe/package.json

@@ -16,8 +16,8 @@
     "test:c8": "c8 $C8_OPTIONS ava --config=ava-nesm.config.js",
     "test:unit": "ava 'test/unitTests' -T 1m --verbose",
     "test:swingset": "ava 'test/swingsetTests' -T 10m --verbose",
-    "test:xs": "yarn test:xs-unit",
-    "test:xs-unit": "ava-xs --verbose",
+    "test:xs": "yarn test:xs-worker",
+    "test:xs-unit": "exit 0",
     "test:xs-worker": "SWINGSET_WORKER_TYPE=xs-worker ava -c 2 'test/swingsetTests'",
     "build-zcfBundle": "yarn build:bundles",
     "lint-fix": "yarn lint:eslint --fix",
@@ -85,52 +85,6 @@
     "exported.js",
     "NEWS.md"
   ],
-  "ava-xs": {
-    "exclude": [
-      "# path/url/import.meta stuff",
-      "unitTests/contracts/",
-      "test/swingsetTests/privateArgs/privateArgs.test.js",
-      "test/swingsetTests/brokenContracts/crashingContract.test.js",
-      "test/swingsetTests/offerArgs/offerArgs.test.js",
-      "test/swingsetTests/makeKind/makeKind.test.js",
-      "test/swingsetTests/zoe/zoe.test.js",
-      "test/swingsetTests/runMint/runMint.test.js",
-      "test/unitTests/zoe.test.js",
-      "test/unitTests/scriptedOracle.test.js",
-      "test/unitTests/makeKind.test.js",
-      "test/unitTests/instanceStorage.test.js",
-      "test/unitTests/contractSupport/depositTo.test.js",
-      "test/unitTests/contractSupport/withdrawFrom.test.js",
-      "test/unitTests/contractSupport/offerTo.test.js",
-      "test/unitTests/zcf/zcfSeat.test.js",
-      "test/unitTests/zcf/zcfSeat-exit.test.js",
-      "test/unitTests/zcf/setupZcfTest.js",
-      "test/unitTests/zcf/feeMintAccess.test.js",
-      "# import.meta.url by way of setupZcfTest",
-      "test/unitTests/zoe.test.js",
-      "test/unitTests/zoe-startInstance.test.js",
-      "test/unitTests/blockedOffers.test.js",
-      "test/unitTests/zcf/reallocate-empty.test.js",
-      "test/unitTests/zcf/zoeHelpersWZcf.test.js",
-      "test/unitTests/zcf/reallocateForZCFMint.test.js",
-      "test/unitTests/zcf/atomicRearrange.test.js",
-      "test/unitTests/zcf/zcf.test.js",
-      "test/unitTests/zcf/allStagedSeatsUsed.test.js",
-      "# ManualTimer.setWakeup: no function",
-      "test/unitTests/fakePriceAuthority.test.js",
-      "test/unitTests/manualTimer.test.js",
-      "# hangs",
-      "makeKind.test.js",
-      "test/unitTests/scriptedOracle.test.js",
-      "test/unitTests/zoe.test.js",
-      "test/unitTests/zcf/allStagedSeatsUsed.test.js",
-      "# t.snapshot",
-      "test/exports.test.js",
-      "test/snapshots",
-      "# We use SWINGSET_WORKER_TYPE=xs ava to run these...",
-      "swingsetTests"
-    ]
-  },
   "ava": {
     "files": [
       "test/**/*.test.*"