[Review] Remove unused CombinedMessage.kt

mirai-core-api/src/commonMain/kotlin/message/data/CombinedMessage.kt

@@ -1,62 +0,0 @@
-/*
- * Copyright 2019-2020 Mamoe Technologies and contributors.
- *
- *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
- *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
- *
- *  https://github.com/mamoe/mirai/blob/master/LICENSE
- */
-
-@file:JvmMultifileClass
-@file:JvmName("MessageUtils")
-
-package net.mamoe.mirai.message.data
-
-//
-///**
-// * 快速链接的两个消息 (避免构造新的 list).
-// *
-// * 不要直接构造 [CombinedMessage], 使用 [Message.plus]
-// * 要连接多个 [Message], 使用 [buildMessageChain]
-// *
-// * @see Message.plus
-// *
-// * Left-biased list
-// */
-//@Serializable
-//internal data class CombinedMessage
-//internal constructor(
-//    @JvmField internal val left: Message, // 必须已经完成 constrain single
-//    @JvmField internal val tail: Message
-//) : Message, MessageChain, List<SingleMessage> by (left.flatten() + tail.flatten()).toList() {
-//    private val toStringCache: String by lazy(NONE) { left.contentToString() + tail.contentToString() }
-//    override fun toString(): String = toStringCache
-//
-//    private val contentToStringCache: String by lazy(NONE) { left.contentToString() + tail.contentToString() }
-//    override fun contentToString(): String = contentToStringCache
-//}
-
-/*
-@JvmSynthetic
-// 不要把它用作 local function, 会编译错误
-
-private suspend fun SequenceScope<SingleMessage>.yieldCombinedOrElementsFlatten(message: Message) {
-    when (message) {
-        is CombinedMessage -> {
-            // fast path
-            yieldCombinedOrElementsFlatten(message.left)
-            yieldCombinedOrElementsFlatten(message.tail)
-        }
-        is MessageChain -> {
-            yieldAll(message)
-        }
-        else -> {
-            check(message is SingleMessage) {
-                "unsupported Message type: ${message::class}" +
-                        "A Message must be a CombinedMessage, a Iterable<Message> or a SingleMessage"
-            }
-            yield(message)
-        }
-    }
-}
-*/