Removing deprecated methods on LinearSolver.

Hello,

Some methods on the MPSolver class have been deprecated for some times now.
These are:

// *** DEPRECATED ***

// Setters and getters for the objective. Please call

// Objective().Getter() and MutableObjective()->Setter() instead.

double objective_value() const;

double best_objective_bound() const;

void ClearObjective();

void SetObjectiveCoefficient(const MPVariable* const var, double coeff);

void SetObjectiveOffset(double value);

void AddObjectiveOffset(double value);

void SetOptimizationDirection(bool maximize);

void SetMinimization() { SetOptimizationDirection(false); }

void SetMaximization() { SetOptimizationDirection(true); }

bool Maximization() const;

bool Minimization() const;

For C++, please use the above fix (calling Objective() or MutableObjective()).

For Python, Java, .NET, there is only Objective (no MutableObjective).

I have ported all examples in the distribution following this change.

I am sorry as this will break you project. But I hope everybody agrees that keeping a minimal API is worth it.