Removed relayer_account: &AccountId from MessageDispatch (#2080)
* SourceBridgeHubChain/TargetBridgeHubChain replaced with RelayerAccountChain * Fix * Removed `relayer_account: &AccountId` from `MessageDispatch`
* SourceBridgeHubChain/TargetBridgeHubChain replaced with RelayerAccountChain * Fix * Removed `relayer_account: &AccountId` from `MessageDispatch`