common/file: Remove [[nodiscard]] from Open()

Since this has a void return value, there's nothing that can actually be
used.

src/common/fs/file.h

@@ -188,8 +188,7 @@ public:
 
 #ifdef _WIN32
     template <typename Path>
-    [[nodiscard]] void Open(const Path& path, FileAccessMode mode,
-                            FileType type = FileType::BinaryFile,
+    void Open(const Path& path, FileAccessMode mode, FileType type = FileType::BinaryFile,
               FileShareFlag flag = FileShareFlag::ShareReadOnly) {
         using ValueType = typename Path::value_type;
         if constexpr (IsChar<ValueType>) {