rpm: do not use "-n" for immutable-object-cache

rpm: do not use "-n" for immutable-object-cache

as immutable-object-cache has the prefix of "ceph", no need to use "-n"
option. so this change is but a cleanup.

* use "%package immutable-object-cache" not "%package
  ceph-immutable-object-cache" for naming subpackage of
  "ceph-immutable-object-cache". this would result in package name of
  "ceph-immutable-object-cache". see
  http://ftp.rpm.org/max-rpm/s1-rpm-subpack-spec-file-changes.html
* the same applies to other directives with "-n" options, see
  http://ftp.rpm.org/max-rpm/s1-rpm-inside-package-directive.html

Signed-off-by: Kefu Chai <kchai@redhat.com>