remove additional f18 references

f18 has been EOL for 6 weeks now, time to purge it from devstack

Change-Id: I5aac2c63b2f4cd8b01ae685b1acf4c188637558b
diff --git a/files/rpms/glance b/files/rpms/glance
index 25c5d39..c886ece 100644
--- a/files/rpms/glance
+++ b/files/rpms/glance
@@ -9,8 +9,8 @@
 python-devel
 python-eventlet
 python-greenlet
-python-lxml         #dist:f18,f19,f20,rhel7
-python-paste-deploy #dist:f18,f19,f20,rhel7
+python-lxml         #dist:f19,f20,rhel7
+python-paste-deploy #dist:f19,f20,rhel7
 python-routes
 python-sqlalchemy
 python-wsgiref