["When applicable, unstable sorting is preferred because it is generally
faster than stable sorting and it doesn’t allocate auxiliary
memory."](https://doc.rust-lang.org/std/vec/struct.Vec.html#method.sort)
Binary also reduced by 1KB in Release.
Testing: No behaviour change as semantically all current usage does not
have any pair with `std::cmp::Ordering::Equal`.
Signed-off-by: Euclid Ye <euclid.ye@huawei.com>