Methane should not depend on gridcell-level TWS

I often run into a situation where a change in some unrelated part of the code causes substantial answer changes to various methane variables. My best guess is that this is because of the dependence of methane on gridcell-level total water storage (TWS):

https://github.com/ESCOMP/ctsm/blob/b26c12f6318c7e7b766b2960f46aec7c56df7941/src/biogeochem/ch4FInundatedStreamType.F90#L306-L307

This is problematic for two reasons:

1. Scientifically, we shouldn't have column-level quantities depending on gridcell-level quantities. The way the code currently operates, a change in, say, the glacier portion of a gridcell causes significant answer changes in the vegetated column in that grid cell.

2. This causes extra time in going through test results for many tags where we expect small answer changes in some limited hydrology fields. These kinds of tags are common right now, so the current operation of this code causes technical debt.

After some deliberation, I have decided to label this as "bug - other". I do believe that point (1) indicates a bug. However, I doubt this has a substantial impact on the scientific results of the model.