[Doc] Misc fix for doc (#3782)

* Update nn-pytorch.rst

* Update dgl.data.rst

* Update dgl.rst

docs/source/api/python/dgl.data.rst

@@ -83,8 +83,6 @@ Datasets for graph classification/regression tasks
     LegacyTUDataset
     GINDataset
     FakeNewsDataset
-    AsNodePredDataset
-    AsEdgePredDataset
 
 Dataset adapters
 -------------------

docs/source/api/python/dgl.rst

@@ -28,6 +28,7 @@ Operators for constructing :class:`DGLGraph` from raw data formats.
     segmented_knn_graph
     create_block
     block_to_graph
+    merge
 
 .. _api-subgraph-extraction:
 

docs/source/api/python/nn-pytorch.rst

@@ -34,6 +34,7 @@ Conv Layers
     ~dgl.nn.pytorch.conv.TWIRLSConv
     ~dgl.nn.pytorch.conv.TWIRLSUnfoldingAndAttention
     ~dgl.nn.pytorch.conv.GCN2Conv
+    ~dgl.nn.pytorch.conv.HGTConv
 
 Dense Conv Layers
 ----------------------------------------