[Bugfix] Fix feature type of 'ENZYMES' in TUDataset (#2800)

* PPIDataset

* Revert "PPIDataset"

This reverts commit 264bd0c960cfa698a7bb946dad132bf52c2d0c8a.

* Hide implementations that may cause confusions to the user

* fix number of classes in Amazon Cobuy datasets

* add four papers

* fix feature type of TU dataset

* fix readme

* remove commented codes
Co-authored-by: Minjie Wang <wmjlyjemaine@gmail.com>

python/dgl/data/tu.py

@@ -324,7 +324,7 @@ class TUDataset(DGLBuiltinDataset):
         for filename, field_name in self.attr_dict.items():
             try:
                 data = loadtxt(self._file_path(filename),
-                               delimiter=',').astype(int)
+                               delimiter=',')
                 if 'label' in filename:
                     data = F.tensor(self._idx_from_zero(data))
                 else: