delete unused dispose

[pixelzoom]

Related to #30 (code review).

It looks like instances of RutherfordAtomNode and RSBaseModel exist for the lifetime of the sim, and their dispose functions are never exercised. If that's indeed the case, then recommend to delete code related to dispose, and simply add a comment that instances of these types exist for the lifetime of the sim.

In general:
• For common code, always implement dispose, unless you are implement something that can only exist for the lifetime of the sim.
• For sim-specific code, implement dispose only for types that don't exist for the lifetime of the sim. Otherwise you're writing code unnecessary code that's never exercised and therefore never tested.

[pixelzoom]

👍 Closing.