Revert "Upgrade virtualenv in pre"

Reverts temporary.

This reverts commit 241e34748dabec12b7043924cb1628ed9bbbde48.

Change-Id: I4af6b9c57e594fce407b9524f04cfa83479e16f0

tests/pre.yml

@@ -17,11 +17,6 @@
         managed_network_prefix_length: "{{ api_network_prefix_length }}"
         managed_network_address_family: "{{ address_family }}"
   tasks:
-    # TODO(mnasiadka): Remove once infra merges virtualenv fixes
-    - name: Upgrade virtualenv package
-      command: python3 -m pip install -U virtualenv
-      become: True
-
     - name: Ensure /tmp/logs/ dir
       file:
         path: "{{ logs_dir }}"