Remove setting nonexistant [ec2] driver option in keystone

There's no [ec2] driver option in keystone.

Change-Id: Ifee92127f32db85d4d55f665471c8da1c9a970e7
diff --git a/lib/keystone b/lib/keystone
index 976aad0..a1d832c 100644
--- a/lib/keystone
+++ b/lib/keystone
@@ -248,7 +248,6 @@
     fi
 
     iniset $KEYSTONE_CONF database connection `database_connection_url keystone`
-    iniset $KEYSTONE_CONF ec2 driver "keystone.contrib.ec2.backends.sql.Ec2"
 
     iniset $KEYSTONE_CONF token driver "$KEYSTONE_TOKEN_BACKEND"