remove the hive dashboard's stats page and the price table behind it

The ST4TS page (/stats.html), GET /api/stats-hive, hive-c0re's hive_stats
rollup and the modelPrices option that only fed its cost estimate are
gone. Each agent's own /stats page and the turn-stats database it reads
are unchanged. Setting modelPrices now fails evaluation with a message
saying so.

hive-c0re/src/socket_server/mod.rs

@@ -577,7 +577,6 @@ mod tests {
         let coord = Coordinator::open(
             &dir.path().join("broker.sqlite"),
             crate::coordinator::HiveEnv::default(),
-            crate::hive_stats::PriceTable::new(),
             1,
         )
         .expect("open coordinator");