key_manager: Remove unnecessary seek in DeriveSDSeed()

Given the file is opened a few lines above and no operations are done,
other than check if the file is in a valid state, the read/write pointer
will always be at the beginning of the file.

src/core/crypto/key_manager.cpp

@@ -152,7 +152,6 @@ boost::optional<Key128> DeriveSDSeed() {
     if (!sd_private.IsOpen())
         return boost::none;
 
-    sd_private.Seek(0, SEEK_SET);
     std::array<u8, 0x10> private_seed{};
     if (sd_private.ReadBytes(private_seed.data(), private_seed.size()) != 0x10)
         return boost::none;