generateSignInWithEmailLink is still dependant on Dynamic Links

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

* Operating System version: N/A
* Firebase SDK version: 13.4.0
* Firebase Product: auth
* Node.js version: N/A
* NPM version: N/A

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

In the latest Admin SDK (13.4.0) version `generateSignInWithEmailLink` appears to still be dependant on Dynamic Links and `actionCodeSettings.linkDomain` doesn't seem to be doing anything.

When I use the method in a Firebase project with Dynamic Links set up, the generated link follows the `https://.page.link?...` format.

And when I try and use in in a project with Dynamic Links not set up, I get the following error:
```
FirebaseAuthError: FDL domain is not configured Raw server response: "{"error":{"code":400,"message":"DYNAMIC_LINK_NOT_ACTIVATED : FDL domain is not configured","errors":[{"message":"DYNAMIC_LINK_NOT_ACTIVATED : FDL domain is not configured","domain":"global","reason":"invalid"}]}}"
```