[Dataset] CoraFull dataset remove redundant reference (#2172)

* PPIDataset

* Revert "PPIDataset"

This reverts commit 264bd0c960cfa698a7bb946dad132bf52c2d0c8a.

* Update gnn_benckmark.py

python/dgl/data/gnn_benckmark.py

@@ -143,9 +143,7 @@ class CoraFullDataset(GNNBenchmarkDataset):
         >>> dataset = CoraFullDataset()
         >>> graph = dataset[0]
 
-    Extended Cora dataset from `Deep Gaussian Embedding of Graphs:
-    Unsupervised Inductive Learning via Ranking`.
-    Nodes represent paper and edges represent citations.
+    Extended Cora dataset. Nodes represent paper and edges represent citations.
 
     Reference: `<https://github.com/shchur/gnn-benchmark#datasets>`_