leaudio: Remove old LC3 encoder

New LC3 is already use some time and no major issue was found.
Therefore making it default

Bug: 150670922
Tag: #feature
Sponsor: jpawlowski@
Test: atest --host bluetooth_le_audio_test bluetooth_le_audio_client_test
Change-Id: Ib4a3a58c762abd384bb64a4804c9562643ced789