Document that auth.deleteUsers() does not trigger auth.user().onDelete() in the docstring

### [REQUIRED] Step 2: Describe your environment

* Operating System version: NA
* Firebase SDK version: 13.4.0
* Firebase Product: auth (node.js admin sdk)
* Node.js version: 20
* NPM version: NA

### [REQUIRED] Step 3: Describe the problem

The deleteUsers() API does not trigger auth.user().onDelete() function calls for each individually deleted user.

This was unexpected for me, and the issue here is that this behavior was not documented in the place where I looked: the function docstring.

After https://github.com/firebase/firebase-functions/issues/860, I can see that this behavior was documented here https://firebase.google.com/docs/auth/admin/manage-users#delete_multiple_users

However, it is not documented on the actual function docstring: https://github.com/firebase/firebase-admin-node/blob/3c2cb9f0265ae836469198a7ff18d5454f18aefd/src/auth/base-auth.ts#L456-L469 (which is used to generate the API reference version at https://firebase.google.com/docs/reference/admin/node/firebase-admin.auth.baseauth#baseauthdeleteusers)

I would have preferred to see the same warning there, since this is what appears in IDEs when you may be poking around for a bulk version of `deleteUser()`.