platforms/rdn2: remove model parameter 'force_rnsam_internal'

The model parameter 'css.cmn_kampos.force_rnsam_internal' has been
renamed as 'css.cmn700.force_rnsam_internal' and has been made an
optional model parameter. So remove this parameter from the
run_model script for rdn2 platform.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: Ib68e11ccc078e0f62d63b8d1868f2a7c5f7b6bee