fix(utils): medusa internal service returned data should match typings (#12715)

FIXES SUP-1824

**What**
The medusa internal service update should always return the data in the expected shape described by the interface. The medusa service should not have to handle the reshapre

packages/modules/customer/src/services/customer-module.ts

@@ -218,7 +218,7 @@ export default class CustomerModuleService
       populate: true,
     })
 
-    return isString(idsOrSelector) ? serialized[0] : serialized
+    return serialized
   }
 
   // @ts-expect-error