update layers/index.rst and layers/index_en.rst (#7135)

Author: Echo-Nie

docs/api_guides/low_level/layers/index.rst

@@ -5,16 +5,10 @@
 ..  toctree::
     :maxdepth: 1
 
-    conv.rst
-    pooling.rst
-    detection.rst
-    sequence.rst
-    math.rst
     activations.rst
-    loss_function.rst
-    data_in_out.rst
     control_flow.rst
-    sparse_update.rst
-    data_feeder.rst
+    conv.rst
     learning_rate_scheduler.rst
-    tensor.rst
+    loss_function.rst
+    pooling.rst
+    sparse_update.rst

docs/api_guides/low_level/layers/index_en.rst

@@ -5,16 +5,10 @@ Neural Network Layer
 ..  toctree::
     :maxdepth: 1
 
-    conv_en.rst
-    pooling_en.rst
-    detection_en.rst
-    sequence_en.rst
-    math_en.rst
     activations_en.rst
-    loss_function_en.rst
-    data_in_out_en.rst
     control_flow_en.rst
-    sparse_update_en.rst
-    data_feeder_en.rst
+    conv_en.rst
     learning_rate_scheduler_en.rst
-    tensor_en.rst
+    loss_function_en.rst
+    pooling_en.rst
+    sparse_update_en.rst