improve HFP logging

- Change log level from error to warning when a device does not have a state machine. This is a normal condition when LE audio device is active and HFP device set to null.
- remove non-necessary debug log

Bug: 352165574
Change-Id: Ib7253afae383538914beb6a4790cae32513dfb8d
Test: m packages/modules/Bluetooth
Flag: exempt, logging change