Clarify and Clean Up Use of Klf in CFE

[robertbartel]

As discussed in NOAA-OWP/ngen#220, all the CFE implementations currently use an expressly provided value for Klf - the lateral flow parameter for the soil reservoir. The value is either hard-coded or an external configuration parameter. However, there are several things that suggest this is not how CFE should function.

Code was written for deriving the Klf value from other parameter values:

// Equation 10 in parameter equivalence document.
lateral_flow_linear_reservoir_constant=2.0*assumed_near_channel_water_table_slope*NWM_soil_params.mult*
                                       NWM_soil_params.satdk*NWM_soil_params.D*drainage_density_km_per_km2;   // m/s
lateral_flow_linear_reservoir_constant*=3600.0;  // convert to m/h

Further, in the latest revision of the original stand-alone version, this is the line where the soil reservoir struct's member variable for Klf is set:

soil_reservoir.coeff_secondary=0.01; // 0.0 to deactiv. else =lateral_flow_linear_reservoir_constant; // m per h

Clarification is needed on how this should be implemented, with the code adjusted if needed and any misleading/unnecessary comments and code cleaned up.

[hellkite500]

@madMatchstick Would you take a quick look at this in relation to the current noaa-owp/CFE code and see if this is still relevant to the current state of the code there? If so, we may want to migrate this issue.