This aims to make future refactoring easier. The arguments are removed where possible, but kept and marked with C++17's [[maybe_unused]] where they could not be removed (e.g. when they are used as a callback, rather than called directly).
I've skipped the rides/<category>/* and peep/* source files, because the rides source files are mostly generated and have a ton of unused variables, and the peep source files are being refactored.
I've also skipped most of window/* source files, because most of the functions are used as callbacks and will be bulk-renamed at some point.
Prior to the previous commit, signs could be duplicated by pasting them using the tile inspector, which results in some funky behaviour. A duplicated sign refers to the same banner index (which in turn refers to the same user string ID), making the player unable to modify it. Deleting it would previously even crash the game.
This commit looks for such signs when loading a scenario, and attempts to fix them, by creating a new banner entry (and user string if one is used).
