clean up instances of "self" that are not used in closures

[jbphet]

In the "Coding Style Guidelines" of the "PhET Development Overview" document, it says:

If references are needed to the enclosing object, such as for a closure, ‘self’ should be used, but it should only be used in closures. The ‘self’ variable should not be defined unless it is needed in a closure.

I'm seeing some places in the code where self is being defined and is not being used in closures. This should be cleaned up.

[aadish]

fixed, closing