Android: Add common function for adding/releasing native reference

webrtc/sdk/android/src/jni/pc/mediasource_jni.cc

Index: webrtc/sdk/android/src/jni/pc/mediasource_jni.cc
diff --git a/webrtc/sdk/android/src/jni/pc/mediasource_jni.cc b/webrtc/sdk/android/src/jni/pc/mediasource_jni.cc
index 6e3150d3fbeb7939337aa7700a76c071393ba918..0771b76fd009cf4ace5dc38c43d090b6566901ea 100644
--- a/webrtc/sdk/android/src/jni/pc/mediasource_jni.cc
+++ b/webrtc/sdk/android/src/jni/pc/mediasource_jni.cc
@@ -13,10 +13,6 @@
 
 namespace webrtc_jni {
 
-JNI_FUNCTION_DECLARATION(void, MediaSource_free, JNIEnv*, jclass, jlong j_p) {
-  reinterpret_cast<rtc::RefCountInterface*>(j_p)->Release();
-}
-
 JNI_FUNCTION_DECLARATION(jobject,
                          MediaSource_nativeState,
                          JNIEnv* jni,