fix(core): cross region ssm writer update (aws#23356)

Hello,
I have come across many errors with cross region export feature when updating the export values.
Without this fix when updating cross region export values and there are no ssm parameters to be deleted, the Lambda function would throw with error:
```
ERROR	Error processing event:  AccessDeniedException: User: arn:aws:sts::xxx:assumed-role/xxx-CustomCrossRegionExportWrite-xxx/xxx-CustomCrossRegionExportWrite-xxx is not authorized to perform: ssm:DeleteParameters on resource: arn:aws:ssm:us-east-1:xxx:* because no identity-based policy allows the ssm:DeleteParameters action
    at Request.extractError (/var/runtime/node_modules/aws-sdk/lib/protocol/json.js:52:27)
    at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:106:20)
    at Request.emit (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:78:10)
    at Request.emit (/var/runtime/node_modules/aws-sdk/lib/request.js:686:14)
    at Request.transition (/var/runtime/node_modules/aws-sdk/lib/request.js:22:10)
    at AcceptorStateMachine.runTo (/var/runtime/node_modules/aws-sdk/lib/state_machine.js:14:12)
    at /var/runtime/node_modules/aws-sdk/lib/state_machine.js:26:10
    at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:38:9)
    at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:688:12)
    at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:116:18) {
  code: 'AccessDeniedException',
  time: 2022-12-15T10:13:59.977Z,
  requestId: 'xxx',
  statusCode: 400,
  retryable: false,
  retryDelay: 10.941837950279254
}}
```
This is because `ssm.deleteParameters` would be called with empty array for `Names` parameter as:
```js
await ssm.deleteParameters({
  Names: [],
}).promise();
```

----

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/core/lib/custom-resource-provider/cross-region-export-providers/cross-region-ssm-writer-handler/index.ts

@@ -30,9 +30,13 @@ export async function handler(event: AWSLambda.CloudFormationCustomResourceEvent
         const removedExports = except(oldExports, exports);
         await throwIfAnyInUse(ssm, removedExports);
         // if the ones we are removing are not in use then delete them
-        await ssm.deleteParameters({
-          Names: Object.keys(removedExports),
-        }).promise();
+        // skip if no export names are to be deleted
+        const removedExportsNames = Object.keys(removedExports);
+        if (removedExportsNames.length > 0) {
+          await ssm.deleteParameters({
+            Names: removedExportsNames,
+          }).promise();
+        }
 
         // also throw an error if we are creating a new export that already exists for some reason
         await throwIfAnyInUse(ssm, newExports);

packages/@aws-cdk/core/test/custom-resource-provider/cross-region-ssm-writer-handler.test.ts

@@ -177,6 +177,7 @@ describe('cross-region-ssm-writer entrypoint', () => {
       });
       expect(mockPutParameter).toHaveBeenCalledTimes(1);
       expect(mocklistTagsForResource).toHaveBeenCalledTimes(1);
+      expect(mockDeleteParameters).toHaveBeenCalledTimes(0);
     });
 
     test('removed exports are deleted', async () => {