[cleanup] remove deposit refunds
Before fees for native deposit txs were deducted in the ante handler, they were deducted in the deposit handler. This required returning a nil error to cosmos so the fee deduction would be committed. In these error cases we also needed to refund the coins we had previously deposited to a module if necessary.
This refund logic is no longer needed. Errors from the internal handlers, etc can be propagated to cosmos which will discard any store changes (e.g. the coin transfer). Ante will have already deducted the fee.