Remove explicit install of setuptools

This is for an old pip workaround which may no longer be valid.

Change-Id: I0b5e392d58828929f3d18569e77337fb79d93c0f
diff --git a/tox.ini b/tox.ini
index dfa8332..e2a9b3f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,7 +11,6 @@
     BRANCH_NAME=master
     CLIENT_NAME=tempest
 deps =
-    setuptools
     -r{toxinidir}/requirements.txt
 
 [testenv]