Editor presents legacy Android push settings as active Firebase configuration

**Describe the bug (REQUIRED)**
`extension-push` reads `android.gcm_sender_id` and `android.fcm_application_id`, passes them to Java, and checks whether they are empty. However, their values are not used to configure Firebase; `getToken()` uses `google-services.xml`. The empty checks also incorrectly use `== ""` instead of `.isEmpty()`.

It is therefore unclear whether these settings are required or obsolete.

Relevant code:

- https://github.com/defold/extension-push/blob/master/extension-push/src/push_android.cpp#L511-L517
- https://github.com/defold/extension-push/blob/master/extension-push/src/java/com/defold/push/Push.java#L417-L427

**To Reproduce (REQUIRED)**

1. Configure Firebase using `google-services.xml`.
2. Leave both project settings empty.
3. Call `push.register()`.

**Expected behavior (REQUIRED)**
Since current extension-push uses google-services.xml, remove these reads and checks from the extension and remove the corresponding Defold project settings.

**Defold version (REQUIRED):**

- 1.13.2

**Platforms (REQUIRED):**

- Platforms: Android
- OS: Android
- Device: Any

**Workaround (OPTIONAL):**
Set both fields while also providing `google-services.xml`.

Start with extension-push/src/push_android.cpp around lines 511-517 and extension-push/src/java/com/defold/push/Push.java around lines 417-427, then locate the corresponding Defold project settings. Reproduce registration with google-services.xml and both settings empty; done means the legacy reads and checks and their project settings are removed without affecting Firebase configuration.

Written by the indexing model from the issue text.