Remove feegrant module - #3958

Clean, thorough removal of the feegrant module: the fee-granter rejection is correctly placed at a single choke point (Tx.ValidateBasic, reached by both CosmosStatelessChecks and ValidateBasicDecorator), the v6.7 module-version delete is needed because SetModuleVersionMap is additive, and no dangling references remain. No blockers; a few non-blocking notes on flatkv store deletion, ante-level test coverage, historical tx decodability, and the 0x1010 "deterministic revert" claim.