Removing unnecessary parameters

[jkiviluo]

From discussion in Amsterdam: In some places in the model variables are multiplied with a parameter to indicate whether it's needed or not. This is extra work for the presolver and could be avoided. This will be possible at least for static parameters and for time-varying parameters in single shot models.

[clizbe]

@jkiviluo Can you specify how this can be avoided? And do we know how much we would gain from doing this?