CLEANUP: channel: Remove channel_htx_copy_msg() function

This function is now unused. So it is removed.
diff --git a/include/proto/channel.h b/include/proto/channel.h
index 88f4f25..175d311 100644
--- a/include/proto/channel.h
+++ b/include/proto/channel.h
@@ -932,22 +932,6 @@
 	return pos;
 }
 
-/* Copy an HTX message stored in the buffer <msg> to the channel's one. We
- * take care to not overwrite existing data in the channel. All the message is
- * copied or nothing. It returns 1 on success and 0 on error.
- */
-static inline int channel_htx_copy_msg(struct channel *chn, struct htx *htx, const struct buffer *msg)
-{
-	/* The channel buffer is empty, we can do a raw copy */
-	if (c_empty(chn)) {
-		chn->buf.data = msg->data;
-		memcpy(chn->buf.area, msg->area, msg->data);
-		return 1;
-	}
-
-	/* Otherwise, we need to append the HTX message */
-	return htx_append_msg(htx, htxbuf(msg));
-}
 /*
  * Advance the channel buffer's read pointer by <len> bytes. This is useful
  * when data have been read directly from the buffer. It is illegal to call