fix warnings: some more easy cases

bffhd/capnp/authenticationsystem.rs

@@ -113,7 +113,7 @@ impl AuthenticationSystem for Authentication {
                 f.write_char(')')
             }
         }
-        let mut response;
+        let response;
 
         let mut builder = results.get();
         if let State::Running(mut session, manager) =

bffhd/capnp/permissionsystem.rs

@@ -36,7 +36,7 @@ impl PermissionSystem for Permissions {
 
         tracing::trace!("method call");
         let roles = self.roles.list().collect::<Vec<&String>>();
-        let mut builder = results.get();
+        let builder = results.get();
         let mut b = builder.init_role_list(roles.len() as u32);
         for (i, role) in roles.into_iter().enumerate() {
             let mut role_builder = b.reborrow().get(i as u32);

bffhd/capnp/user.rs

@@ -221,7 +221,7 @@ impl card_d_e_s_fire_e_v2::Server for User {
                 Vec::new()
             });
         if !tk.is_empty() {
-            let mut b = results.get();
+            let b = results.get();
             let mut lb = b.init_token_list(1);
             lb.set(0, &tk[..]);
         }