Merge branch 'revert_mpas_noopenacc' into ew-develop (PR #22)

Fix correctness issues by reverting MPAS-A to a v7.3 version without
OpenACC directives.

NOTE: This will require cases using cam_dev physics to have
'use_gw_front = .false.' in user_nl_cam (if not already present).

Externals_CAM.cfg

@@ -66,9 +66,9 @@ required = True
 [mpas]
 local_path = src/dynamics/mpas/dycore
 protocol = git
-repo_url = https://github.com/EarthWorksOrg/MPAS-Model.git
+repo_url = https://github.com/MPAS-Dev/MPAS-Model.git
 sparse = ../.mpas_sparse_checkout
-tag = mpasa-ew2.2.000
+hash = ff76a231
 required = True
 
 [geoschem]