refactor(web/panettone): Remove prevalence

Now that we've migrated over all the data to postgresql, we can get rid
of cl-prevalence as a dependency from Panettone along with all code that
mentions it.

Change-Id: I945f50a88fea5770aac5b4a058342b8269c0bea2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1495
Reviewed-by: kanepyork <rikingcoding@gmail.com>
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

ops/nixos/panettone.nix

@@ -70,13 +70,11 @@ in {
       serviceConfig = {
         DynamicUser = true;
         Restart = "always";
-        StateDirectory = "panettone";
         EnvironmentFile = cfg.secretsFile;
       };
 
       environment = {
         PANETTONE_PORT = toString cfg.port;
-        PANETTONE_DATA_DIR = "/var/lib/panettone";
         PGHOST = "localhost";
         PGUSER = cfg.dbUser;
         PGDATABASE = cfg.dbName;