rest_flag is allowed in build-namelist, but not in the FORTRAN namelist

[ekluzek]

Brief summary of bug

The namelist item "rest_flag" to turn off restart handling is allowed in build-namelist at the preview_namelist level -- but not in the Fortran code. So using it is allowed at preview_namelist, but it dies at runtime.

General bug information

CTSM version you are using: ctsm5.3.061-6-ga27de36fe
Does this bug cause significantly incorrect results in the model's science? No

Configurations affected: Only when you set rest_flag in user_nl_clm

Details of bug

It's only defined in namelist definition as follows...

<entry id="rest_flag" type="logical" category="clm_restart"
       group="clm_inparm" valid_values="" >
If FALSE, don't write any restart files.
</entry>

From git blame, I added this back in 2008-2010. I am not sure why.

Important details of your setup / configuration so we can reproduce the bug

It dies with the usual namelist issue in controlMod.F90:

 Attempting to initialize run control settings .....
 Read in clm_inparm namelist from: lnd_in
 ENDRUN:
 ERROR reading clm_inparm namelistERROR in /glade/work/erik/ctsm_worktrees/cleanupwork/src/main/controlMod.F90 at line 377

[ekluzek]

I was thinking this would be useful for self-tests. But, since we can turn off restarts with

REST_OPTION="none"

for cases, that's really the way to do this. And possibly the history of this is that it was removed in the code because of the overall CESM control. So the remnants of this should just be removed.