[Doc] remove duplicate papers (#3393)

* remove duplicate paper

* Update README.md

README.md

@@ -246,14 +246,6 @@ Take the survey [here](https://forms.gle/Ej3jHCocACmb49Gp8) and leave any feedba
 
 1. [**Enhancing Scientific Papers Summarization with Citation Graph**](https://arxiv.org/abs/2104.03057), AAAI'21, *Chenxin An, Ming Zhong, Yiran Chen, Danqing Wang, Xipeng Qiu, Xuanjing Huang*
 
-1. [**Graph Ensemble Learning over Multiple Dependency Trees for Aspect-level Sentiment Classification**](https://arxiv.org/abs/2103.11794), NAACL'21, *Xiaochen Hou, Peng Qi, Guangtao Wang, Rex Ying, Jing Huang, Xiaodong He, Bowen Zhou*
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-1. [**Enhancing Scientific Papers Summarization with Citation Graph**](https://arxiv.org/abs/2104.03057), AAAI'21, *Chenxin An, Ming Zhong, Yiran Chen, Danqing Wang, Xipeng Qiu, Xuanjing Huang*
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-1. [**Graph Ensemble Learning over Multiple Dependency Trees for Aspect-level Sentiment Classification**](https://arxiv.org/abs/2103.11794), NAACL'21, *Xiaochen Hou, Peng Qi, Guangtao Wang, Rex Ying, Jing Huang, Xiaodong He, Bowen Zhou*
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-1. [**Enhancing Scientific Papers Summarization with Citation Graph**](https://arxiv.org/abs/2104.03057), AAAI'21, *Chenxin An, Ming Zhong, Yiran Chen, Danqing Wang, Xipeng Qiu, Xuanjing Huang*
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 1. [**Improving Graph Representation Learning by Contrastive Regularization**](https://arxiv.org/pdf/2101.11525.pdf), *Kaili Ma, Haochen Yang, Han Yang, Tatiana Jin, Pengfei Chen, Yongqiang Chen, Barakeel Fanseu Kamhoua, James Cheng*
 
 1. [**Extract the Knowledge of Graph Neural Networks and Go Beyond it: An Effective Knowledge Distillation Framework**](https://arxiv.org/pdf/2103.02885.pdf), WWW'21, *Cheng Yang, Jiawei Liu, Chuan Shi*