leaudio: Fix update metadata

Update Metadata can be done on ASEs in Enabling and Streaming state.
It metadata update happen when 1st earbud was streaming and second was
joining the stream, stack could incorrectly send Metadata Update in
invalid ASE state.

Note, this patch also removes dead code, which is a loop never executed.

Bug: 261538915
Test: atest bluetooth_le_audio_test
Test: atest BluetoothInstrumentationTests
Tag: #feature
Change-Id: I07b6152d6f1672dc8efb77054bb7ff147fcc2a80