hotfix Bug 1499 - deleted flow still present

StatisticManager needs to delete the statistics and the flows too.
* fix a path to delete whole flow (no only statistics)

Note: bugfix could help for bug 1345 too.

Change-Id: I8a8bee995d42daa9f1832cc8e26cc2c02b2e64c1
Signed-off-by: Vaclav Demcak <vdemcak@cisco.com>