Remove compset backwards compatibility once all components have been updated

[billsacks]

Once these three issues are resolved:

• After updating to cism2_1_76 or later, change compsets involving CISM CESM#181
• After updating to cism2_1_76 or later, change compsets involving CISM CAM#340
• After updating to cism2_1_76 or later, change compsets involving CISM CTSM#1289

Then we should remove the compset backward compatibility code from config_component.xml. Search for BACKWARDS_COMPATIBILITY in that file for things to remove.