Remove unused variable, rename internal variable

[ColCarroll]

This is just tidying up some of the covariance adaptation code. It should not change any behavior, just makes things a little more readable.

I left a few things in so the QuadPotentialDiagAdaptGrad can be worked on in the future.

[junpenglao]

I am not sure if we should make this change, IIUC the weight is for potentially adding a decaying weighting like exponential. Although right now weight=1 but I imagine removing it will make doing experiment more difficult (although nobody is actually doing these kind of experiment currently).

[ColCarroll]

Agree -- I'll roll that back, but leave some of the other changes in. I consider this a promise that you'll continue these experiments, though!

[junpenglao]

I will put it in my OKR for the next quarter 😂

[rpgoldman]

@ColCarroll Any reason not to merge this?

[ColCarroll]

Should be good now!