build: pare down vendored proto definitions

[conorsch]

As of #99, we're using vendored proto definitions from the Penumbra monorepo. The initial inclusion of proto defs copied them over from the Penumbra repo. Instead, we should be using the buf-tooling to fetch the info that we need. We also don't need all those protos, like tendermint, ibc, etc. It should be enough to fetch-and-then-vendor only the specific proto defs that we need.

One way to do this is to fetch via buf export and then rm -rf <dir> and dirs we don't care about. See similar logic in:

• https://github.com/penumbra-zone/penumbra/blob/82962431d5f28c03fb5acfe1075a2ecf37f8337f/deployments/scripts/protobuf-codegen
• https://github.com/cosmos/relayer/blob/df42391dd3ab04fce238adb7b4112d7bd10fa63c/scripts/protocgen.sh

We could also wire up CI to publish the Galileo protos, but I don't think that's necessary, and would prefer to avoid it until it's must-do for some reason.

[cratelyn]

thank you for filing this! i'd love to avoid the need to vendor these, i appreciate your grace in allowing me to be expeditious and hacky 🙏