Remove sv_unlockedchapters cvar

[vrad-exe]

Which component should be improved?

Other

Describe your suggestion

sv_unlockedchapters was used in HL2 era games to store the player's chapter unlock progress, but it doesn't do anything anymore in Portal 2, with chapter progress instead being stored using a hardcoded "title data" system. When the P2CE chapter progression system is eventually rebuilt, it needs to support user created campaigns including having multiple installed at once, and therefore can't use a single cvar, so this should just be removed.

Momentum lacks the concept of chapters entirely, so it also doesn't need this, but still has it currently.

[craftablescience]

Some mods might use this cvar to store data or control other things, I don't see any harm in leaving it around