Remove ALL of the POP ocean grids and ocean masks

[ekluzek]

Once, #207 happens and components have changed their testing. We will be able to remove all of the POP ocean grids and ocean masks as the last vestiges of having POP in CESM.

This is dependent on issues that are in other components: CTSM, RTM, MOSART, CMEPS, CISM, and CAM.

POP grids include: gx37, gx17, gx16, tx.01v2, tx0.1v3

Definition of done:

• Remove gx1v6
• Figure out if there are alias combinations that can be removed
• Remove any aliases that can be removed
• Remove tx.01v2 when CAM VR grids move away from it
• Remove tx.01v3 when CAM mpas and VR grids move away from it.

[ekluzek]

It looks like because some CAM grids are using tx.01v2 as well as tx.01v3, we can't get rid of them yet. It will need to wait until CAM moves away from them. gx1v6 looks safe to remove though. And we can likely remove some alias combinations.

See the CAM issue here:

ESCOMP/CAM#1236 (comment)