Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)

If Rich Presence and Discord Presence are enabled in Achievement Settings, the string generated by rcheevos as the player's current Rich Presence will be sent to the Status field in the Discord Presence object. This will be updated whenever Rich Presence updates.

/home/ports/pobj/dolphin-5.0.0.20230429/dolphin-5.0.0.20230429/Source/Core/UICommon/DiscordPresence.cpp:27:13: warning: unused variable 's_using_custom_client' [-Wunused-variable]
static bool s_using_custom_client = false;
            ^

Otherwise, files that include the header get warning: ‘Discord::s_using_custom_client’ defined but not used.