Make --audio-codec=raw the default

Encoding and decoding the audio stream adds latency, which is not ideal
for real-time mirroring.

PR #3757 <https://github.com/Genymobile/scrcpy/pull/3757>

app/scrcpy.1

@@ -35,7 +35,7 @@ Default is 0 (no buffering).
 .BI "\-\-audio\-codec " name
 Select an audio codec (raw, opus or aac).
 
-Default is opus.
+Default is raw.
 
 .TP
 .BI "\-\-audio\-encoder " name