Audio codecs API: Remove some weasel words in the docs

These things are no longer brand new, so it makes even less sense
than it once did to warn users that they may change at any time.

Bug: none
Change-Id: I43a6915d9e00fbfef30fdb89869873b129297c8d
No-Try: true
Reviewed-on: https://webrtc-review.googlesource.com/c/106980
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25283}

api/audio_codecs/L16/audio_encoder_L16.h

@@ -24,8 +24,6 @@ namespace webrtc {
 
 // L16 encoder API for use as a template parameter to
 // CreateAudioEncoderFactory<...>().
-//
-// NOTE: This struct is still under development and may change without notice.
 struct RTC_EXPORT AudioEncoderL16 {
   struct Config {
     bool IsOk() const {