Removed XREF to old blog entry in Ceph section

Removed reference to old blog entry (06/2012) in "Ceph RADOS Block
Device (RBD)" section of Config Reference Guide.

I only removed the paragraph that qualified the blog entry as a source
of "detailed installation instructions". The entry mentions 'nova
volume', which is no longer in use AFAIK.

Change-Id: Id996909f0568e74fa59c2f99044ad61e49d4760c
Closes-Bug: #1279132
Merge "Removed XREF to old blog entry in Ceph section"