TMS causes SGH30 to be written to restart uneccesarily

@elynnwu discovered this when running a restart w/ latest master but with an older restart file. The restart initialization went looking for SGH in the restart file.

A little digging found that in TMS, SGH30 is a "required" field. For initialization this isn't an issue because the driver initializes SGH30 from the topography file. But at restart the logic instead goes looking for this variable in the restart file. Currently, it is also written to the restart file, so the bug won't impact any runs. But we should probably fix this because a typical user won't expect that SGH30 is being grabbed from a restart instead of the topo file, and we want to avoid writing fields to restart that don't need to be there.