Remove DocImpact info from contributor docs

[OpenStack Infra]

https://review.openstack.org/503710
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/neutron" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit 81c0c347e31bd6ee46089c733035b281b646a955
Author: Brian Haley <email address hidden>
Date: Wed Sep 13 09:21:32 2017 -0600

    Remove DocImpact info from contributor docs

    As discussed at Denver PTG, DocImpact tag will be retired.
    Feature patch must now include relevant documentation changes.

    Change-Id: I6aa3753772321733920481ac57549a648f92c6de

[Slawek Kaplonski (slaweq)]

I think that it is made just by mistake. In commit message there was info about removing "DocImpact" so it was "false-positive" IMO. If no, please reopen it.