Delete unused methods for replacing the "default filesystem".

Bug: webrtc:6424
Change-Id: I7f76fe71ac395088c3b632e43475933cc13e47cd
Reviewed-on: https://webrtc-review.googlesource.com/83725
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23728}
diff --git a/rtc_base/fileutils.cc b/rtc_base/fileutils.cc
index 0037547..7d83f97 100644
--- a/rtc_base/fileutils.cc
+++ b/rtc_base/fileutils.cc
@@ -117,17 +117,14 @@
 #endif
 }
 
-FilesystemInterface* Filesystem::default_filesystem_ = nullptr;
-
-FilesystemInterface* Filesystem::EnsureDefaultFilesystem() {
-  if (!default_filesystem_) {
+FilesystemInterface* Filesystem::GetFilesystem() {
 #if defined(WEBRTC_WIN)
-    default_filesystem_ = new Win32Filesystem();
+  static FilesystemInterface* const filesystem = new Win32Filesystem();
 #else
-    default_filesystem_ = new UnixFilesystem();
+  static FilesystemInterface* const filesystem = new UnixFilesystem();
 #endif
-  }
-  return default_filesystem_;
+
+  return filesystem;
 }
 
 }  // namespace rtc