libgsm's "gsm.h" is now C++-safe.

Test: treehugger
Change-Id: I9efbde5677111d0b13ff5ec814b1d0f5037937d4
diff --git a/src/jni/rtp/GsmCodec.cpp b/src/jni/rtp/GsmCodec.cpp
index 4a04bfa..ff1acec 100644
--- a/src/jni/rtp/GsmCodec.cpp
+++ b/src/jni/rtp/GsmCodec.cpp
@@ -16,9 +16,7 @@
 
 #include "AudioCodec.h"
 
-extern "C" {
 #include "gsm.h"
-}
 
 namespace {