Remove mention of mongodb
Remove mention of mongodb

MongoDB is no longer necessary to run Spectrometer. Remove all mention
of it in docs.

Change-Id: I4a72a4f0565821a5e19ee94fecfc44d91ffaa552
Signed-off-by: Thanh Ha <09ea4d3a79c8bee41a16519f6a431f6bc0fd8d6f@linuxfoundation.org>

opendaylight/spectrometer,opendaylight/spectrometer,opendaylight/spectrometer,opendaylight/spectrometer