Build a mechanism to identify withdrawn provisional media types

[halostatue]

#53 reworks the handling of the provisional media type registry in order to avoid a duplicate error on application/netcdf (see #50).

However, since types/provisional-standard-types.yaml has been removed, there is no way to see if types were removed from the provisional registry because the standard or the provisional registration was withdrawn. (The current handling should properly handle upgrades from provisional to registration.)

In order to keep the data clean, we need to resolve this.