fix: remove unused aws-lambda package to eliminate aws-sdk v2 dependency (github-aws-runners#5088)

## Summary

The `aws-lambda` npm package
([npmjs.com/package/aws-lambda](https://www.npmjs.com/package/aws-lambda))
is a CLI deploy tool last published in November 2021. It is listed as a
production dependency in `webhook` and `aws-powertools-util`, but **is
not used anywhere at runtime**.

Every `import` from `'aws-lambda'` in the codebase (e.g. `import {
Context, SQSEvent } from 'aws-lambda'`) resolves to `@types/aws-lambda`
— TypeScript type definitions that are erased at compile time.
`@types/aws-lambda` is already correctly declared as a `devDependency`
in all packages that use it.

### Why this matters

The `aws-lambda` package transitively depends on `aws-sdk@^2.814.0`
(v2), which reached end-of-support on September 8, 2025. Advisory
[GHSA-j965-2qgj-vjmq](GHSA-j965-2qgj-vjmq)
flags all of aws-sdk v2 with no patch available — the only remediation
is migrating to v3. This causes the **Dependency vulnerability scan** to
fail on any PR that modifies the lockfile enough to trigger a dependency
graph rebuild.

### What this PR does

- Removes `aws-lambda` from `dependencies` in
`lambdas/functions/webhook/package.json` and
`lambdas/libs/aws-powertools-util/package.json`
- Regenerates `yarn.lock`, eliminating `aws-sdk` v2 and its transitive
dependency tree from the lockfile

### What this PR does NOT do

- Does not change any source code — no runtime behavior changes
- Does not remove `@types/aws-lambda` (the TypeScript types) — those
remain as devDependencies

## Test plan

- [x] All 352 tests pass (`yarn test` across all 7 projects)
- [x] Dependency vulnerability scan should now pass (no more aws-sdk v2
in the dependency graph)

Author: jensenbox

lambdas/functions/webhook/package.json

@@ -34,8 +34,7 @@
     "@middy/core": "^6.4.5",
     "@octokit/rest": "22.0.1",
     "@octokit/types": "^16.0.0",
-    "@octokit/webhooks": "^14.2.0",
-    "aws-lambda": "^1.0.7"
+    "@octokit/webhooks": "^14.2.0"
   },
   "nx": {
     "includedScripts": [

lambdas/libs/aws-powertools-util/package.json

@@ -22,8 +22,7 @@
   "dependencies": {
     "@aws-lambda-powertools/logger": "^2.31.0",
     "@aws-lambda-powertools/metrics": "^2.31.0",
-    "@aws-lambda-powertools/tracer": "^2.31.0",
-    "aws-lambda": "^1.0.7"
+    "@aws-lambda-powertools/tracer": "^2.31.0"
   },
   "nx": {
     "includedScripts": [