Remove code that's actually unused. (#3574)

Fixes #3574

Signed-off-by: YunKui Lu <luyunkui95@gmail.com>
(cherry picked from commit 3b94838)

Author: YunKuiLu

spring-ai-model/src/main/java/org/springframework/ai/model/tool/DefaultToolCallingManager.java

@@ -153,10 +153,6 @@ private static ToolContext buildToolContext(Prompt prompt, AssistantMessage assi
 				&& !CollectionUtils.isEmpty(toolCallingChatOptions.getToolContext())) {
 			toolContextMap = new HashMap<>(toolCallingChatOptions.getToolContext());
 
-			List<Message> messageHistory = new ArrayList<>(prompt.copy().getInstructions());
-			messageHistory.add(new AssistantMessage(assistantMessage.getText(), assistantMessage.getMetadata(),
-					assistantMessage.getToolCalls()));
-
 			toolContextMap.put(ToolContext.TOOL_CALL_HISTORY,
 					buildConversationHistoryBeforeToolExecution(prompt, assistantMessage));
 		}