FilePlayer: Remove unused default values for arguments

The functions in question were virtual, so we would've wanted to get
rid of the default values even if callers had relied on them.

Review-Url: https://codereview.webrtc.org/2045943004
Cr-Commit-Position: refs/heads/master@{#13800}
diff --git a/webrtc/modules/utility/include/file_player.h b/webrtc/modules/utility/include/file_player.h
index 5f79fd2..508c211 100644
--- a/webrtc/modules/utility/include/file_player.h
+++ b/webrtc/modules/utility/include/file_player.h
@@ -57,16 +57,16 @@
                                    uint32_t startPosition,
                                    float volumeScaling,
                                    uint32_t notification,
-                                   uint32_t stopPosition = 0,
-                                   const CodecInst* codecInst = NULL) = 0;
+                                   uint32_t stopPosition,
+                                   const CodecInst* codecInst) = 0;
 
   // Note: codecInst is used for pre-encoded files.
   virtual int32_t StartPlayingFile(InStream& sourceStream,
                                    uint32_t startPosition,
                                    float volumeScaling,
                                    uint32_t notification,
-                                   uint32_t stopPosition = 0,
-                                   const CodecInst* codecInst = NULL) = 0;
+                                   uint32_t stopPosition,
+                                   const CodecInst* codecInst) = 0;
 
   virtual int32_t StopPlayingFile() = 0;