Fix Load Wii System Menu not updating after performing a disc update

[Pokechu22]

This fixes an annoying case where installing the system menu via "Perform System Update" on a disc would fail to enable the Load Wii System Menu item in the tools menu until Dolphin is restarted. If a system menu was already installed, then the old version would still be displayed, but the button was usable.

I also replace the call the "Perform Online Update" function uses to avoid this with a more general one. Note that NANDRefresh is connected to UpdateToolsMenu:

dolphin/Source/Core/DolphinQt/MenuBar.cpp

Line 265 in 0461170

connect(&Settings::Instance(), &Settings::NANDRefresh, [this] { UpdateToolsMenu(false); });