Fix Baichuan chat template

[Dinghow]

The previous template_baichuan.jinja generates extra \n compared with official implementation.

Given the input messages is

[
    {'role': 'user', 'content': 'Hello, who are you'},
    {'role': 'assistant', 'content': 'I am a large language model from Baichuan Inc'},
    {'role': 'user', 'content': "What's the capital of Canada?"},
]

The text generated by the official version:
<reserved_106>Hello, who are you<reserved_107>I am a large language model from Baichuan Inc<reserved_106>What's the capital of Canada?<reserved_107>

while previous template_baichuan.jinja:
\n\n<reserved_106>\nHello, who are you\n\n<reserved_107>\nI am a large language model from Baichuan Inc\n\n<reserved_106>\nWhat's the capital of Canada?<reserved_107>\n

This PR fix the jinja template based on the official version.

[Dinghow]

@simon-mo also cc this?