L-17. Remove `x/audit` module

[linear]

Drop AuditKeeper references in x/market and the BidFilter adapter; handler collapses back to a single verification call. Upgrade handler prunes the store via StoreUpgrades.Deleted. Remove AttributesFilters from PlacementRequirements at the next major SDK bump (separately; don't break old SDLs in this chain upgrade).

Depends on: L-16

DoD: x/audit is gone from app.go; build green; audit store pruned; no x/audit/AttributesFilters references in node or provider.