Move FATES regression test mod definitions from HLMs to FATES testing subdirectory?

[glemieux]

My idea for this came up in the wake of testing #1273. This pull request removes some history output variables. This resulted in a test run failure as the testmod was asking specifically for some of the tests that were specifically requested. If we move the test mod definitions from the host land models into the fates testing subdirectory, we could avoid the need to create a HLM-side PR for fates pulls in which we remove history output.

[glemieux]

@rgknox FYI we talked about this in the CTSM software meeting on Jan 9 while you were away. The consensus is that decoupling fates test definitions from the HLM is the ideal way to go about doing this. I've inquired with the CIME team via Slack to run the idea up the flag poll before seriously pursuing an update.