auth: remove unused permissions field from cache role_record

The permissions field in role_record was populated by fetch_role() but
never read. Authorization uses cached_permissions instead, which is
loaded via the permission_loader callback. Remove the dead field and
its fetch code.

The removed code also did not check for missing columns before accessing
the permissions set, which could crash on ghost rows left by the removed
auth v2 migration. The migration used INSERT (creating row markers),
and when permissions were later revoked, the row marker survived while
the permissions column became null.

(cherry picked from commit 797bc28aae)

auth/cache.cc

@@ -190,19 +190,6 @@ future<lw_shared_ptr<cache::role_record>> cache::fetch_role(const role_name_t& r
             co_await coroutine::maybe_yield();
         }
     }
-    // permissions
-    {
-        static const sstring q = format("SELECT role, resource, permissions FROM {}.{} WHERE role = ?", db::system_keyspace::NAME, PERMISSIONS_CF);
-        auto rs = co_await fetch(q);
-        for (const auto& r : *rs) {
-            auto resource = r.get_as<sstring>("resource");
-            auto perms_strings = r.get_set<sstring>("permissions");
-            std::unordered_set<sstring> perms_set(perms_strings.begin(), perms_strings.end());
-            auto pset = permissions::from_strings(perms_set);
-            rec->permissions[std::move(resource)] = std::move(pset);
-            co_await coroutine::maybe_yield();
-        }
-    }
     co_return rec;
 }
 

auth/cache.hh

@@ -44,7 +44,6 @@ public:
         std::unordered_set<role_name_t> members;
         sstring salted_hash;
         std::unordered_map<sstring, sstring, sstring_hash, sstring_eq> attributes;
-        std::unordered_map<sstring, permission_set, sstring_hash, sstring_eq> permissions;
     private:
         friend cache;
         // cached permissions include effects of role's inheritance