fix(cli): SynthUtils is not used (#9836)

unused imports makes the jsii fail because jsii has no chill.

```
.test.ts:1:45 - error TS6133: 'SynthUtils' is declared but its value is never read.
1 import { expect as expectCDK, haveResource, SynthUtils } from '@aws-cdk/assert';
                                              ~~~~~~~~~~
```
----

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packages/aws-cdk/lib/init-templates/lib/typescript/test/%name%.test.template.ts

@@ -1,4 +1,4 @@
-import { expect as expectCDK, haveResource, SynthUtils } from '@aws-cdk/assert';
+import { expect as expectCDK, haveResource } from '@aws-cdk/assert';
 import * as cdk from '@aws-cdk/core';
 import * as %name.PascalCased% from '../lib/index';