refactor(promise-kit): depend on harden, not ses (#3108)

Closes: #XXXX
Refs: #3107

## Description

`@endo/promise-kit` is a tiny package that had depended on `'ses'` only
for `harden`. It is a great example of why we factored `harden` out into
an importable `@endo/harden`. The PR changes `@endo/promise-kit` to
depend directly on `endo@harden` rather than `ses`.

### Security Considerations

none

### Scaling Considerations

A bit. It means other packages can depend on @endo/promise-kit without
bringing in all of ses.

### Documentation Considerations

none

### Testing Considerations

- [x] Should do the multi-ses-ava mode testing that @kriskowal set up.
Addendum: happy to find that it already happens without my needing to do
anything. Thanks @kriskowal !

### Compatibility Considerations

none

### Upgrade Considerations

none

Author: erights

.changeset/fancy-pots-enjoy.md

@@ -0,0 +1,5 @@
+---
+'@endo/promise-kit': patch
+---
+
+`@endo/promise-kit` no longer depends on `ses`, just `@endo/harden`

packages/promise-kit/package.json

@@ -37,8 +37,7 @@
     "test:xs": "exit 0"
   },
   "dependencies": {
-    "@endo/harden": "workspace:^",
-    "ses": "workspace:^"
+    "@endo/harden": "workspace:^"
   },
   "devDependencies": {
     "ava": "catalog:dev",

yarn.lock

@@ -1091,7 +1091,6 @@ __metadata:
     ava: "catalog:dev"
     c8: "catalog:dev"
     eslint: "catalog:dev"
-    ses: "workspace:^"
     typescript: "npm:~5.9.2"
   languageName: unknown
   linkType: soft