Use PhysicalConstantsDictionary instead of CIME shared constants for Omega

[xylar]

In E3SM-Project/Omega#288, Omega will begin using constants from https://github.com/E3SM-Project/PhysicalConstantsDictionary for things such as the Earth radius. We should figure out how to migrate Polaris as well. Questions are:

• how do we give Polaris access to the yaml file? Should we make tags and conda packages of PhysicalConstantsDictionary?
• do we need distinct values for Omega vs. MPAS-Ocean? How does that work with the Earth radius in particular?