osu! rejects modified DLL at first

[holly-hacker]

Often when replacing the original DLL with a custom one, osu! will force update because it detected modified game files. Closing the game after the update and replacing the DLL again will fix this, but it is still inconvenient.

This is likely related to file hashes stored in osu!.cfg. Clearing them when we're changing the DLL may fix the issue.