Revert "Workaround to install specific version of dogpile.cache"

This reverts commit 310f3e3.

Depends-On: https://review.openstack.org/#/c/625759/
Change-Id: I3d42233240e1eb09fdf1831d1bc31681b3b77ae7

ansible/install/roles/rally/tasks/main.yml

@@ -15,12 +15,6 @@
     line: 'export REQUESTS_CA_BUNDLE={{ overcloud_ca_path }}'
   when: overcloud_ca_path is defined
 
-- name: Temporary workaround to avoid conflicts with dogpile.cache
-  pip:
-    name: dogpile.cache
-    version: 0.6.8
-    virtualenv: "{{ rally_venv }}"
-
 - name: Install Rally with OpenStack plugins into rally-venv
   pip:
     name: rally-openstack