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

web/panettone/default.nix

@@ -4,7 +4,6 @@ depot.nix.buildLisp.program {
   name = "panettone";
 
   deps = with depot.third_party.lisp; [
-    cl-prevalence
     cl-who
     drakma
     defclass-std