S2 width depends on drift time, not depth

[tunnell]

The 'z' parameter is corrected depth:

https://github.com/XENON1T/hax/blob/master/hax/treemakers/corrections.py#L35

The width cut is defined on this corrected z. Diffusion depends on drift time. This was caught by @rafaellang.

[tunnell]

Use from Basics the drift_time variable.

[zhut19]

I do realize using drift time is the correct definition, but drift time don't reflect the ~2us that electron took to drift from gate to liquid level, which would have a different diffusion model. (However, z already subtracted this part)

[rafaellang]

How about adding those 2us to drift time as a constant offset?

[pdeperio]

Fixed in #134