It was deprecated at [1], and quota of resource will be registered
at initialization of APIRouter. So, no need to use the config now.
[1] https://review.openstack.org/#/c/181593
DocImpact: All references of 'quota_items' configuration option
and its description should be removed from the docs.
UpgradeImpact: Remove 'quota_items' configuration option from
neutron.conf file.
Change-Id: I0698772a49f51d7c65f1f4cf1ea7660cd07113a0
Closes-Bug: #1593772