does Equation needs a dispose method?

[pixelzoom]

Game creates 5 of these when level selection button is pressed.

[pixelzoom]

Equation does not currently need dispose. It links to Properties of its reactants and products:

    this.reactants.forEach( reactant => reactant.userCoefficientProperty.lazyLink( observer ) );
    this.products.forEach( product => product.userCoefficientProperty.lazyLink( observer ) );

... but Equation is an abstract base class, and the reactants and products are own owned by the subclasses. So there is no need to call dispose for any instance of Equation.

It will likely need dispose if/when instrumented for PhET-iO.

[samreid]

I detected a TODO for this issue as part of phetsims/chipper#946 and decided to remove the TODO.