Remove deprecated FSRef-manipulation methods.

The replacement methods had already been added to applefilesystem.mm, they just
weren't being used on macOS.

BUG=webrtc:6028

Review-Url: https://codereview.webrtc.org/2395593002
Cr-Commit-Position: refs/heads/master@{#14535}
diff --git a/webrtc/base/unixfilesystem.h b/webrtc/base/unixfilesystem.h
index dbfbaf0..78351e8 100644
--- a/webrtc/base/unixfilesystem.h
+++ b/webrtc/base/unixfilesystem.h
@@ -22,7 +22,7 @@
   UnixFilesystem();
   ~UnixFilesystem() override;
 
-#if defined(WEBRTC_ANDROID) || defined(WEBRTC_IOS)
+#if defined(WEBRTC_ANDROID) || defined(WEBRTC_MAC)
   // Android does not have a native code API to fetch the app data or temp
   // folders. That needs to be passed into this class from Java. Similarly, iOS
   // only supports an Objective-C API for fetching the folder locations, so that
@@ -113,7 +113,7 @@
   Pathname GetCurrentDirectory() override;
 
  private:
-#if defined(WEBRTC_ANDROID) || defined(WEBRTC_IOS)
+#if defined(WEBRTC_ANDROID) || defined(WEBRTC_MAC)
   static char* provided_app_data_folder_;
   static char* provided_app_temp_folder_;
 #else