Common/IOFile: Remove the Duplicate function. The duplicate handles shared a read/write position making them effectively not thread-safe.

Source/Core/Common/IOFile.cpp

@@ -101,15 +101,6 @@ bool IOFile::Close()
   return m_good;
 }
 
-IOFile IOFile::Duplicate(const char openmode[]) const
-{
-#ifdef _WIN32
-  return IOFile(_fdopen(_dup(_fileno(m_file)), openmode));
-#else   // _WIN32
-  return IOFile(fdopen(dup(fileno(m_file)), openmode));
-#endif  // _WIN32
-}
-
 void IOFile::SetHandle(std::FILE* file)
 {
   Close();

Source/Core/Common/IOFile.h

@@ -51,8 +51,6 @@ public:
             SharedAccess sh = SharedAccess::Default);
   bool Close();
 
-  IOFile Duplicate(const char openmode[]) const;
-
   template <typename T>
   requires(std::is_trivially_copyable_v<T>)
   bool ReadArray(T* elements, size_t count, size_t* num_read = nullptr)