No longer need to allow for C/E at end of time period

[billsacks]

Description of changes

We are changing the compset specification to no longer have C/E at the end of the time period, so we can remove the parsing of this from compset regexes.

Needs to wait for the compset changes in
ESCOMP/CESM#407 and
ESCOMP/CAM#1584.

Specific notes

Contributors other than yourself, if any: none

CTSM issues resolved or otherwise addressed, if any:

• Fixes Change how CLM_CO2_TYPE is set from the compset longname #4078

Any user interface changes (namelist or namelist defaults changes)? no

Testing planned or performed, if any:
none yet

Requirements before merge:

• I have followed the CTSM contribution guidelines.

• The code in this PR branch builds with no errors.
• The code in this PR branch runs with no errors. Briefly describe tested configuration(s):
• This either (a) does not change answers, (b) it only changes answers at roundoff level, or (c) I have performed a scientific evaluation of the answer changes. Which?:

• I have reviewed relevant parts of the CLM documentation Tech Note or User's Guide to determine if anything needs to be changed or added. If it does, describe:
• This PR either (a) does not create a need to update the documentation or (b) includes required documentation updates (see guidelines for contributing documentation). Which?:

[billsacks]

Blocked / dependency: Needs to wait for the compset changes in ESCOMP/CESM#407 and ESCOMP/CAM#1584 before coming in to a CESM alpha tag or a CAM tag.

[ekluzek]

I did some checking to make sure there wasn't anywhere else to change, and didn't find anything. So this will be good to go, once the other changes are in.