Delete geomagio/Metadata.py

geomagio/Metadata.py was used to temporarily "simulate" an instrument calibration metadata service. I replaced this months ago in !311 (merged) but didn't delete Metadata.py. Leaving geomagio/Metadata.py in this repo creates confusion with /geomagio/metadata/Metadata.py so it needs to go.

I verified that there are no longer any imports that reference this file. And the information that it contains has been uploaded to the metadata servers.