Clean up CI

[juliasloan25]

After SDI #281 , the runtime of our CI pipeline increased from ~1h42m to ~2h20m. This slowdown is likely due to changes in ClimaAtmos associated with the update to v0.11.0. While this is unavoidable on our end, we still want to keep our CI as streamlined as possible. We also had to add increased slurm_mem limits for AMIP tests, which should eventually be removed. This would be a good time to go through the CI and clean up/remove any unnecessary tests or environments that won't be maintained moving forward.

Issue #299 addresses the replacement of the experiments/AMIP/moist_mpi_earth directory with experiments/AMIP/modular.

[juliasloan25]

no longer needed - see #406