[qt, settings] allow to set custom unit and battery serial (#2813)

Also removes "use dev keys" option since it's not even present on UI and it's just a file redirection anyways
Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/2813
Reviewed-by: Caio Oliveira <caiooliveirafarias0@gmail.com>
Reviewed-by: crueter <crueter@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/core/crypto/key_manager.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -311,7 +314,6 @@ private:
     std::array<u8, 576> eticket_extended_kek{};
     RSAKeyPair<2048> eticket_rsa_keypair{};
 
-    bool dev_mode;
     void LoadFromFile(const std::filesystem::path& file_path, bool is_title_keys);
 
     template <size_t Size>