Fully remove the CRU datm forcing option

[ekluzek]

The DATM%CRU_ option still has a few vestiges in place, and should be removed to remove uneeded complexity. I don't think it's fully specified and at this point if you really want the old CRU data you should use the slightly newer CRUv7 version.

Looking in cesm3_0_beta05 it's not in testing, so there's no reason to keep it around. The only relevant references I see for it are in datm/cime_config/config_component.xml

cd datm/cime_config
git grep -w CRU
config_component.xml:    <desc atm="DATM[%QIA][%WISOQIA][%CRU][%CRUv7][%GSWP3v1][%MOSARTTEST][%NLDAS2][%CPLHIST][%1PT][%NYF][%IAF][%JRA][%JRA-1p4-2018][%JRA-1p5-2023][%JRA-RYF8485][%JRA-RYF9091][%JRA-RYF0304][%SIMPLE]"> Data driven ATM </desc>
config_component.xml:    <desc option="CRU"> CRUNCEP data set </desc>
config_component.xml:    <desc option="CRUv7"> CLM CRU NCEP v7 data set </desc>
config_component.xml:      <value compset="1850.*_DATM%CRU">1</value>
config_component.xml:      <value compset="HIST.*_DATM%CRU">1901</value>
config_component.xml:      <value compset="20TR.*_DATM%CRU">1901</value>
config_component.xml:      <value compset="SSP.*_DATM%CRU">$DATM_YR_START</value>
config_component.xml:      <value compset="1850.*_DATM%CRU">1</value>
config_component.xml:      <value compset="1850.*_DATM%CRU">1901</value>
config_component.xml:      <value compset="HIST.*_DATM%CRU">1901</value>
config_component.xml:      <value compset="20TR.*_DATM%CRU">1901</value>
config_component.xml:      <value compset="SSP.*_DATM%CRU" >2001</value>
config_component.xml:      <value compset="1850.*_DATM%CRU">1901</value>
config_component.xml:      <value compset="2000.*_DATM%CRU">1991</value>
config_component.xml:      <value compset="2003.*_DATM%CRU">2002</value>
config_component.xml:      <value compset="2010.*_DATM%CRU">2005</value>
config_component.xml:      <value   compset="1850.*_DATM%CRU">1920</value>
config_component.xml:      <value   compset="HIST.*_DATM%CRU">1920</value>
config_component.xml:      <value   compset="20TR.*_DATM%CRU">1920</value>
config_component.xml:      <value   compset="SSP.*_DATM%CRU">2016</value>
config_component.xml:      <value   compset="1850.*_DATM%CRU">1920</value>
config_component.xml:      <value   compset="2000.*_DATM%CRU">2010</value>
config_component.xml:      <value   compset="2003.*_DATM%CRU">2003</value>
config_component.xml:      <value   compset="2010.*_DATM%CRU">2014</value>