Summary/Motivation:

This PR modifies the PyROS solver preprocessor's treatment of second-stage equality constraints that are state-variable independent, for cases wherein the user-supplied uncertainty set is discrete (or scenario-based). Every such constraint is now treated as follows:

• The decision rule expressions are substituted for the second-stage variables
• For each of the (finitely many, hard-coded) scenarios in the uncertainty set, a duplicate of the constraint subject to the scenario is appended to the first-stage equality constraints
• The constraint is removed from the model

That is, when the uncertainty set is discrete, these equality constraints are no longer reformulated by casting to two inequalities (which increases the number of separation problems) or polynomial coefficient matching (which may be restrictive).

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