dev-handbook/x86: remove line numbers from the example

These line numbers seem to be mistakenly copied from the editor.
Since the user is (likely) going to copy-and-paste the example,
we should remove these line numbers.

Reviewed by: Mina Galić <freebsd@igalic.co>, dbaio
Pull Request: https://github.com/freebsd/freebsd-doc/pull/333
Signed-off-by: rilysh <nightquick@proton.me>