Migrate CISM's dlnd usage to new GCPL mode and then remove legacy SCPL mode

In #364, @mvertens introduced a new GCPL mode for dlnd that uses coupler-history output from CMEPS. For now she has left the old SCPL mode in place, and we can't remove it yet because CISM still uses this old SCPL mode. The SCPL mode is set up to use coupler-history output from the mct-based cpl7.

Steps needed are the following (it's possible I'm missing something):
1. Create cplhist forcings for T compsets using a recent version of CESM
2. Update the dlnd config_component to point to these new forcings
3. Change CISM's T compset definitions to use DLND%GCPL mode rather than SCPL
4. Remove references to SCPL and glc_forcing_mct from dlnd

@Katetc I'm assigning this to you because you seem to be the best person to take care of this. There isn't any urgency on this, but it's something that should be dealt with at some point, probably in the run-up to CESM3.