Fix units designations of GW drag diagnostic variables dusfcg, dtaux2d, etc.

[mdtoyNOAA]

This PR corrects the units designations of the gravity wave drag diagnostics variables dusfcg, dvsfcg, dtaux3d and dtauy3d as follows:

The units for the “dusfcg” and “dvsfcg” variables are currently “Pa m s^{-1}” when they actually should simply be “Pa”. These variables represent the vertical integral of “d(tau)/dz”, which turns out to be the GWD at the surface, whose units are “Pa”.

The units for the “dtaux” and “dtauy” variables are currently “m s^{-1}” when they actually should be “m s^{-2}”. These variables represent the vertical divergence of the horizontal GWD momentum flux ( (-1/rho) * d(tau)/dz ), where tau is the GWD momentum flux or “wave stress” (units are Pascal).

This code change is text only, and does not change the model results.

[weiwangncar]

The regression test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None