frappix: bump to 474adcf, drop insights mysqlclient override

Upstream now ships mysqlclient with insights (kurogeek/frappix 474adcf).

pkgs/frappix/overlay.nix

@@ -2,15 +2,8 @@
 # Must be applied after frappixFrappeOverlay (needs prev.frappix).
 final: prev: {
   frappix = prev.frappix.overrideScope (
-    ffinal: fprev: {
+    ffinal: _fprev: {
       default_thai_company = ffinal.callPackage ./default-thai-company.nix { };
-
-      # insights' after_migrate hook opens the "Site DB" data source via
-      # ibis.mysql, whose backend imports MySQLdb (mysqlclient) since ibis 10.
-      # Upstream frappix only ships ibis-framework without the mysql extra.
-      insights = fprev.insights.overridePythonAttrs (old: {
-        dependencies = old.dependencies ++ [ final.python3.pkgs.mysqlclient ];
-      });
     }
   );
 }