Update SEMANTICS.md About Sub Messages

[loloicci]

Although https://github.com/CosmWasm/cosmwasm/blob/main/SEMANTICS.md describe that Response has messages field and submessages field (https://github.com/CosmWasm/cosmwasm/blob/main/SEMANTICS.md#basic-execution), latest cosmwasm's Response does not have mesages field (

cosmwasm/packages/std/src/results/response.rs

Lines 62 to 86 in 2bd030a

	#[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq, JsonSchema)]
	#[non_exhaustive]
	pub struct Response<T = Empty> {
	/// Optional list of messages to pass. These will be executed in order.
	/// If the ReplyOn variant matches the result (Always, Success on Ok, Error on Err),
	/// the runtime will invoke this contract's `reply` entry point
	/// after execution. Otherwise, they act like "fire and forget".
	/// Use `SubMsg::new` to create messages with the older "fire and forget" semantics.
	pub messages: Vec<SubMsg<T>>,
	/// The attributes that will be emitted as part of a "wasm" event.
	///
	/// More info about events (and their attributes) can be found in [*Cosmos SDK* docs].
	///
	/// [*Cosmos SDK* docs]: https://docs.cosmos.network/main/core/events.html
	pub attributes: Vec<Attribute>,
	/// Extra, custom events separate from the main `wasm` one. These will have
	/// `wasm-` prepended to the type.
	///
	/// More info about events can be found in [*Cosmos SDK* docs].
	///
	/// [*Cosmos SDK* docs]: https://docs.cosmos.network/main/core/events.html
	pub events: Vec<Event>,
	/// The binary payload to include in the response.
	pub data: Option<Binary>,
	}

). And, the following sections of SEMANTICS describes the difference between messages and submessages.

And, SubcallResponse in the following section looks like an outdated name. It is SubMsgResponse now.