remove tool dir

tool/ReadMe.md

-## 工具
-
-keras_to_tf.py : keras转tensorflow脚本  
-pytorch_to_onnx.py : pytorch转onnx脚本

tool/keras_to_tf.py

-#   Copyright (c) 2019  PaddlePaddle Authors. All Rights Reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License"
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.