Trim down large gnomad RocksDB databases

[holtgrewe]

Is your feature request related to a problem? Please describe.
We currently write out information that is never read anywhere, for example the age histogram structure. This takes a lot of space.

Describe the solution you'd like
While we should continue parsing this from VCF and keep support for writing protobuf, we should not write this out to protobuf. This should be a flag in annonars if it is not already.

Describe alternatives you've considered
N/A

Additional context
N/A