This is a helper function. It searches through the linear_internal_list of
the stored flex_prms object, and keeps the first unique appearance
of parameters. For example, when the parameter muc is equal for comp, neutral,
and incomp, the function will provide the info "muc" and "comp", thus
dropping incomp and neutral, where the parameter is the same.
prms_cond_combo(drift_dm_obj)a matrix with two rows. Each column contains a combination of the parameter name and the condition that can be considered unique. Parameter names are stored in the first row, condition labels in the second.
an object of type drift_dm