update(migration): update phone registration steps for migration

- Remove check for provisioning service status.
- Update phone configuration instructions: if the hostname changes, a factory reset is now sufficient for phones to retrieve the new configuration

NethServer/dev#7445

Author: Stell0

docs/tutorial/migration/post_migration.md

@@ -41,9 +41,13 @@ After completing the NethVoice migration from NethServer 7 to NethServer 8, veri
    - Test voicemail access
 
 3. **Phone Registration**
-   - Verify provisioning service running
-   - Reboot test phones and check registration
-   - Update DHCP option 66 if needed for new provisioning server
+   - Update DHCP option 66 if needed for new provisioning server
+   - Reboot phones and check registration
+   - If the NethVoice hostname changed, reset phones to factory defaults. They will automatically retrieve the new configuration from the server
+
+***
+
+**Next Step:** Would you like me to also update the **Troubleshooting** section ("Phones Not Registering") to include the factory reset step for changed hostnames?
 
 ## Telephony Testing {#telephony-testing}