Delete FilesystemInterface::CopyFile.

Only use of this method was to implement the cross-device case of
MoveFile on unix systems.

In turn, only use of the MoveFile method is in
FileRotatingStream::RotateFiles. Since file rotation should never
involve any copying of log data, the MoveFile fallback to copying can
be deleted.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2747373003
Cr-Commit-Position: refs/heads/master@{#17364}
diff --git a/webrtc/base/unixfilesystem.cc b/webrtc/base/unixfilesystem.cc
index d0da709..557c478 100644
--- a/webrtc/base/unixfilesystem.cc
+++ b/webrtc/base/unixfilesystem.cc
@@ -204,12 +204,7 @@
   LOG(LS_VERBOSE) << "Moving " << old_path.pathname()
                   << " to " << new_path.pathname();
   if (rename(old_path.pathname().c_str(), new_path.pathname().c_str()) != 0) {
-    if (errno != EXDEV)
-      return false;
-    if (!CopyFile(old_path, new_path))
-      return false;
-    if (!DeleteFile(old_path))
-      return false;
+    return false;
   }
   return true;
 }
@@ -221,31 +216,6 @@
   return S_ISDIR(st.st_mode);
 }
 
-bool UnixFilesystem::CopyFile(const Pathname &old_path,
-                              const Pathname &new_path) {
-  LOG(LS_VERBOSE) << "Copying " << old_path.pathname()
-                  << " to " << new_path.pathname();
-  char buf[256];
-  size_t len;
-
-  StreamInterface *source = OpenFile(old_path, "rb");
-  if (!source)
-    return false;
-
-  StreamInterface *dest = OpenFile(new_path, "wb");
-  if (!dest) {
-    delete source;
-    return false;
-  }
-
-  while (source->Read(buf, sizeof(buf), &len, nullptr) == SR_SUCCESS)
-    dest->Write(buf, len, nullptr, nullptr);
-
-  delete source;
-  delete dest;
-  return true;
-}
-
 bool UnixFilesystem::IsTemporaryPath(const Pathname& pathname) {
 #if defined(WEBRTC_ANDROID) || defined(WEBRTC_MAC)
   RTC_DCHECK(provided_app_temp_folder_ != nullptr);