[FAB-5204] Doc: Delete pip install docker-compose

This patch deletes description of installing docker-compose by pip.

I propose to install docker-compose by downloading from the GitHub
Releases page [1], not by pip.

- A binary we can download from the GitHub Releases page is stand-alone;
  we don't need to worry about conflict among dependencies of
  docker-compose [2] and other packages for Behave BDD tests
- The official docker-compose document recommends to use virtualenv
  because of dependency conflict if we install by pip [3]
- We don't use pip in devenv/setup.sh to setup a developer environment

Installation details for docker-compose aren't this page as we don't
describe for other prerequisites: git, go, etc.

[1] https://github.com/docker/compose/releases
[2] https://pypi.python.org/pypi/docker-compose
[3] https://docs.docker.com/compose/install/#alternative-install-options

Change-Id: I5e7cdd5a5489c43b2f47d616b1dc4d1491cc2136
Signed-off-by: Yuta Namiki <y-namiki@ak.jp.nec.com>

docs/source/dev-setup/devenv.rst

@@ -49,13 +49,13 @@ Prerequisites
 -  Note: The BIOS Enabled Virtualization may be within the CPU or
    Security settings of the BIOS
 
-``pip``, ``behave`` and ``docker-compose``
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+``pip`` and ``behave``
+~~~~~~~~~~~~~~~~~~~~~~
 
 ::
 
     pip install --upgrade pip
-    pip install behave nose docker-compose
+    pip install behave nose
     pip install -I flask==0.10.1 python-dateutil==2.2 pytz==2014.3 pyyaml==3.10 couchdb==1.0 flask-cors==2.0.1 requests==2.4.3 pyOpenSSL==16.2.0 pysha3==1.0b1 grpcio==1.0.4
 
     #PIP packages required for some behave tests