Remove a leftover audio codec poison immutinty declaration

Bug: webrtc:8396
Change-Id: Id15461db14057dec1ffdd652bdd87ceb7b11496d
Reviewed-on: https://webrtc-review.googlesource.com/c/124482
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26849}
diff --git a/pc/BUILD.gn b/pc/BUILD.gn
index 2763f85..59fe940 100644
--- a/pc/BUILD.gn
+++ b/pc/BUILD.gn
@@ -232,7 +232,6 @@
 
 rtc_source_set("libjingle_peerconnection") {
   visibility = [ "*" ]
-  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   deps = [
     ":peerconnection",
     "../api:create_peerconnection_factory",