remove "redhat-rpm-config" (F21 dependency)
remove "redhat-rpm-config" (F21 dependency)

Commit d5004a380294e05963d4de39007f3336e975fb0f introduced the package
"redhat-rpm-config" to make the Fedora 21 gate job running again.

As we dropped the F21 support in December 2015 with
commit 90bc5867728aafb66b374ae6e6a93318303dcff0 we don't need
this package anymore.

Change-Id: I71b969b7fd6651082451f6c4fd1e01d205771a11

dtroyer/devstack,group-policy/devstack,nawawi/openstack,noironetworks/devstack,richliu/devstack,dtroyer/devstack,samgoon/devstack,noironetworks/devstack,bswartz/devstack,openstack-dev/devstack,dirkmueller/devstack,nawawi/openstack,dirkmueller/devstack,openstack-dev/devstack,bigswitch/devstack,bigswitch/devstack,bswartz/devstack,samgoon/devstack,Mahito/devstack,group-policy/devstack,Mahito/devstack,richliu/devstack