Deprecate and/or remove the demand_scaling parameter to the model building function

[danielolsen]

🚀

• Is your feature request essential for your project?

Describe the workflow you want to enable

No change in user-facing functionality.

Describe your proposed implementation

Remove this parameter and any associated logic, since it relates to old logic (i.e. reduce demand by 5% after each infeasible interval) which is no longer used, now that we have per-bus and per-time-period load shedding.

[BainanXia]

Yeah, this old logic for Matpower should only live in REISE instead of REISE.jl.

[merrielle]

Low priority but very easy