Update required packages for ryu

Sync with the recent reality.

Change-Id: I4c37d09e511f3763d2267267815387bd5c825e0e
Closes-Bug: 1287541
diff --git a/files/apts/ryu b/files/apts/ryu
index e8ed926..9b85080 100644
--- a/files/apts/ryu
+++ b/files/apts/ryu
@@ -1,4 +1,2 @@
-python-gevent
-python-gflags
-python-netifaces
+python-eventlet
 python-sphinx