Revert "Fluentd: add fluent-plugin-concat:1.0.0 gem"
Revert "Fluentd: add fluent-plugin-concat:1.0.0 gem"

This reverts commit 83baad304d359e17a5be3ad1e92f7cd31dc129e0.

The plugin is not used in any deployment tool. Was introduced to make multiline but finally standard multiline was used.
This change removes an unused plugin.

Change-Id: Ie38a876d56846ebdec02fa05707e9d22a02788e6

rahulunair/kolla,nihilifer/kolla,stackforge/kolla,openstack/kolla,rahulunair/kolla,openstack/kolla,stackforge/kolla,stackforge/kolla,nihilifer/kolla