Remove pypi download shield from Readme

Pypi is no longer providing download stats for packages [1].
Removing the shield from our readme.txt.

[1] badges/shields#716

Change-Id: I6679f592e866068752b9c695f7357efb6b59c324

README.rst

@@ -6,10 +6,6 @@ Octavia
     :target: https://pypi.python.org/pypi/octavia/
     :alt: Latest Version
 
-.. image:: https://img.shields.io/pypi/dm/octavia.svg
-    :target: https://pypi.python.org/pypi/octavia/
-    :alt: Downloads
-
 Octavia is an operator-grade open source scalable load balancer for use in
 large OpenStack deployments. It delivers load balancing services on `amphorae
 <http://docs.openstack.org/developer/octavia/main/glossary.html>`_ and