Remove benchmark folder from the master branch. They are stale. (#9085)

official/benchmark/models/shakespeare/README.md

-# Shakespeare character LSTM model
-
-This is an implemention of a simple character LSTM used to generate text.
-
-## Instructions
-
-First download the source data:
-
-```
-wget https://storage.googleapis.com/download.tensorflow.org/data/shakespeare.txt
-```
-
-Note that files other than shakepeare.txt can also be used to train the model to generater other text.
-
-Then train the model:
-
-```python
-python3 shakespeare_main.py --training_data shakespeare.txt \
-    --model_dir /tmp/shakespeare
-```
-
-This will place model checkpoints in `/tmp/shakespeare`, so that we can use them to make predictions.
-
-Then generate predictions:
-
-```python
-python3 shakespeare_main.py --training_data shakespeare.txt \
-    --model_dir /tmp/shakespeare --notrain --predict_context=ROMEO:
-```
-
-Change `--predict_context` and `--predict_length` to suit your needs.

official/benchmark/models/shakespeare/__init__.py

-