This reverts commit 371f093.

Jim Edwards posted the following in my PR:
"although you can remove cpl7 you cannot yet remove mct. However I don't
 expect you to remove any externals in this tag, I will remove them in
 the next tag."

ix clm6_0 defaults and CESM testing issues, add tests to detect these problems

Fix the clm6_0 defaults that were incorrect in ctsm5.2.0. The use-cases needed to be changed to handle clm6_0.
And clm6_0 wasn't handled in the merge of ctsm5.1.dev174 for the two new settings. Simplified the use-cases which
should help prevent these problems in the future. use_init_interp will be set for ctsm5.1 finidat files.

Fix some testing. mksurfdata_esmf and the MKSUIRFDATA test didn't work in a CESM checkout. build-namelist unit tests
weren't going over the use-cases. Also started adding some tests to go over finidat files, but didn't yet capture all of them.
Add some scripts to compare namelists in order to detect namelist issues for physics
version updates, and more easily see namelist changes in one place (bld/unit_testers/cmp_baseline_lnd_in_files,
bld/unit_testers/compare_namelists).

Add some tests to detect issues in CESM and CAM testing (add more tests for cam6.0 forcing, add new IHistClm60BgcCropG
compset). Add a NoAnthro compset to the ctsm_sci testing. Add I1850Clm60Sp test for f09 and f19 to ctsm_sci.

Change NoAnthro compsets to use RTM rather than MOSART. Add science support to some clm6_0 compsets, as was obvious.

slevis resolved conflicts:
bld/unit_testers/build-namelist_test.pl
cime_config/testdefs/ExpectedTestFails.xml