[session] drop useless getter and setter for security
Those function have very few user and does not anything fancy. Internal user now
access tx.read/write_security directly. External user have been blessed with a
writable property. They are only interested in the write part of they did not
used the return of the removed function. They access it through the session
since I prefer the external world to not be aware of Transaction yet.
doc/book usr/share/doc/cubicweb-documentation
doc/html usr/share/doc/cubicweb-documentation
debian/cubicweb-doc usr/share/doc-base/cubicweb-doc