Remove requirements.txt

docs/Installation.md

 ### Install Python and mlagents Package
 
 In order to use ML-Agents toolkit, you need Python 3.6 along with the
-dependencies listed in the [requirements file](../ml-agents/requirements.txt).
+dependencies listed in the [setup.py file](../ml-agents/setup.py).
 Some of the primary dependencies include:
 
 - [TensorFlow](Background-TensorFlow.md)

ml-agents/requirements.txt

-tensorflow==1.7.1
-Pillow>=4.2.1
-matplotlib
-numpy>=1.11.0
-jupyter
-pytest>=3.2.2
-docopt
-pyyaml
-protobuf==3.6.0
-grpcio==1.11.0