Sunset program emissions

[jgur-psyops]

We no longer use the program-driven emissions system, as it has proven easier and more effective to simply airdrop rewards to users OTC vs dealing with the headache of a claims portal. We have not offered emissions though the program in several months.

Remove everything related to emissions, including tests. Replace any emissions-related fields (e.g. emissions_rate, emissions_remaining, etc) with placeholders, and add a permissionless ix for banks and user accounts that zeros out any remaining values in those fields so they can be considered padding in the future.

In particular, this simplifies withdraws, as it was always somewhat annoying to integrators that you had to check if there were any outstanding emissions before you could send a withdraw_all.