Update DemoteFromLayer to use terminate cohorts

[glemieux]

Description:

Refactors terminate_cohorts to call a new subroutine, terminate_cohort, that is called to remove an individual cohort. For more information see: #714 (comment).

Collaborators:

@rgknox @ckoven

Expectation of Answer Changes:

Yes

Checklist:

• My change requires a change to the documentation.
• I have updated the in-code documentation .AND. (the technical note .OR. the wiki) accordingly.
• I have read the CONTRIBUTING document.
• FATES PASS/FAIL regression tests were run
• If answers were expected to change, evaluation was performed and provided

Test Results:

TBD
CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag:

FATES baseline hash-tag:

Test Output:

[glemieux]

This appears to be building and running as expected. Initial baseline comparison appears to be b4b:
/glade/u/home/glemieux/scratch/ctsm-tests/tests_pr829_erpshortcompare1

[rgknox]

all tests nominal: /glade/scratch/rgknox/tests_0228-090015ch