Enhance cli_demo.py

[jinchihe]

Enhance cli_demo.py for following:

1. update coding to gbk to avoid below error while running the script.

SyntaxError: (unicode error) 'utf-8' codec can't decode byte 0xbb in position 0: invalid start byte

2. Remove useless import such as import readline that will cause some compilation errors, although may be a problem with my environment, but this import is useless, just remove that to avoid the problem.
3. Remove useless functions in the script to avoid confuse.

Testing with the PR changes, that's OK, the script works fine now with the update:

# python cli_demo.py
Explicitly passing a `revision` is encouraged when loading a model with custom code to ensure no malicious code has been contributed in a newer revision.
Explicitly passing a `revision` is encouraged when loading a configuration with custom code to ensure no malicious code has been contributed in a newer revision.
Explicitly passing a `revision` is encouraged when loading a model with custom code to ensure no malicious code has been contributed in a newer revision.
[2023-07-23 08:05:52,372] [INFO] [real_accelerator.py:110:get_accelerator] Setting ds_accelerator to cuda (auto detect)
Loading checkpoint shards: 100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 7/7 [00:08<00:00,  1.15s/it]
欢迎使用 ChatGLM2-6B 模型，输入内容即可进行对话，clear 清空对话历史，stop 终止程序

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