stdlib: Remove final decorator from abstract board

@typing.final was not introduced until python3.8.

Change-Id: I65a5f4b5655d2ad80f7b566f9cea8e2371b3be62
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55863
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56246
1 file changed