Incorrect metadata in umfile_utils/stashvar.py

[tammasloughran]

ACCESS-Archiver depends on umfile_utils/stashvar.py, which has erroneous metadata for a stashvar.

The field code 3173 is soil (heterotrophic) respiration on tiles according to @rml599gh.
umfile_utils/stashvar.py has this line for code 3173:
Line 1013 atm_stashvar[3173] = ["QCF INCR: bdy layer negative", "", "", "", ""]
The model output data itself looks to me like it has values that look like soil respiration where the relevant PFTs exist, and probably isn't QCF INCR, whatever that is.

Similar to issue #2, umfile_utils is a NCI system environment module, so finding someone to change this error will be difficult.

[MartinDix]

In the standard UM vn7.3 STASH code 3173 wasn't used, so it was grabbed for this diagnostic. From diagnostics_bl.F90

! Soil respiration on tiles (Kg C/m2/s)
! -----------------------------------------------
! Item 173 - kdcorbin, 10/10
     IF (SF(173,3)) THEN

By UM vn8.4 it'd become used for the QCF INCR field. stashvar.py was originally based on a vn10.6 STASHmaster_A file as used for CM2, so picked up this definition.

Will try to fix in ACCESS-NRI/um2nc-standalone#25