Python: Correct chat completion agent history truncation samples (#12474)

### Motivation and Context

<!-- Thank you for your contribution to the semantic-kernel repo!
Please help reviewers and future users, providing the following
information:
  1. Why is this change required?
  2. What problem does it solve?
  3. What scenario does it contribute to?
  4. If it fixes an open issue, please link to the issue here.
-->
While addressing the developer in this
[discussion](#12450),
I notice that there are a few changes needed to the improve the
truncation history reducer samples of the chat completion agent.

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->
Update the samples.


### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

Author: TaoChenOSU

python/samples/concepts/agents/chat_completion_agent/chat_completion_agent_truncate_history_reducer_agent_chat.py

@@ -39,11 +39,11 @@ async def main():
     reducer_msg_count = 10
     reducer_threshold = 10
 
-    # Create a summarization reducer and clear its history
-    history_truncatation_reducer = ChatHistoryTruncationReducer(
+    # Create a truncation reducer and clear its history
+    history_truncation_reducer = ChatHistoryTruncationReducer(
         target_count=reducer_msg_count, threshold_count=reducer_threshold
     )
-    history_truncatation_reducer.clear()
+    history_truncation_reducer.clear()
 
     # Create our agent
     agent = ChatCompletionAgent(
@@ -53,7 +53,7 @@ async def main():
     )
 
     # Create a group chat using the reducer
-    chat = AgentGroupChat(chat_history=history_truncatation_reducer)
+    chat = AgentGroupChat(chat_history=history_truncation_reducer)
 
     # Simulate user messages
     message_count = 50  # Number of messages to simulate
@@ -65,7 +65,7 @@ async def main():
         # Attempt to reduce history
         is_reduced = await chat.reduce_history()
         if is_reduced:
-            print(f"@ History reduced to {len(history_truncatation_reducer.messages)} messages.")
+            print(f"@ History reduced to {len(history_truncation_reducer.messages)} messages.")
 
         # Invoke the agent and display responses
         async for message in chat.invoke(agent):

python/samples/concepts/agents/chat_completion_agent/chat_completion_agent_truncate_history_reducer_single_agent.py

@@ -28,9 +28,10 @@ async def main():
     reducer_msg_count = 10
     reducer_threshold = 10
 
-    # Create a summarization reducer
+    # Create a truncation reducer
     history_truncation_reducer = ChatHistoryTruncationReducer(
-        service=AzureChatCompletion(), target_count=reducer_msg_count, threshold_count=reducer_threshold
+        target_count=reducer_msg_count,
+        threshold_count=reducer_threshold,
     )
 
     thread: ChatHistoryAgentThread = ChatHistoryAgentThread(chat_history=history_truncation_reducer)