Support GCM ciphers even if ENABLE_EXTERNAL_AUTH is defined.

webrtc/webrtc.gni

Index: webrtc/webrtc.gni
diff --git a/webrtc/webrtc.gni b/webrtc/webrtc.gni
index 96975fae9a4227568632a0fc50932d487cd134ac..0a9d42575d1b93bb31a422fee5ad5feb698008b5 100644
--- a/webrtc/webrtc.gni
+++ b/webrtc/webrtc.gni
@@ -48,10 +48,6 @@ declare_args() {
   # Disable the code for the intelligibility enhancer by default.
   rtc_enable_intelligibility_enhancer = false
 
-  # Enable when an external authentication mechanism is used for performing
-  # packet authentication for RTP packets instead of libsrtp.
-  rtc_enable_external_auth = build_with_chromium
-
   # Selects whether debug dumps for the audio processing module
   # should be generated.
   apm_debug_dump = false