kmod: remove libceph bits

Since there are such tight dependencies between libceph and the other two kernel modules, all three kmod packages (libceph, ceph, and rbd) are now built together as part of the ceph-kmod RPM.

@sandonv, if you have time, I'd appreciate a sanity check that this looks good to you. It appears that this change might already be present in Gitbuilder somehow, since I don't see the libceph references in a recent build, here: http://gitbuilder.sepia.ceph.com/gitbuilder-kmod-rpm-rhel7beta-amd64-basic/log.cgi?log=c9d1614e43e46cf3f370a573ab608476a3fe5ab3