Fix some more nightly errors and remove lint that will become an error by default (#4661)

src/db/models/two_factor.rs

@@ -95,7 +95,7 @@ impl TwoFactor {
                 // We need to make sure we're not going to violate the unique constraint on user_uuid and atype.
                 // This happens automatically on other DBMS backends due to replace_into(). PostgreSQL does
                 // not support multiple constraints on ON CONFLICT clauses.
-                diesel::delete(twofactor::table.filter(twofactor::user_uuid.eq(&self.user_uuid)).filter(twofactor::atype.eq(&self.atype)))
+                let _: () = diesel::delete(twofactor::table.filter(twofactor::user_uuid.eq(&self.user_uuid)).filter(twofactor::atype.eq(&self.atype)))
                     .execute(conn)
                     .map_res("Error deleting twofactor for insert")?;