Revert "bsdinstall: add knob to set ASLR sysctls"

This reverts commit 020f4112559ebf7e94665c9a69f89d21929ce82a.

Because now ASLR is enabled by default for 64-bit architectures
and the purpose of the installation menu is to allow choosing
additional 'mitigation'/'hardening' options that are originally
disabled, remove the ASLR knob from bsdinstall.

Discussed with: emaste
Obtained from: Semihalf
Sponsored by: Stormshield

(cherry picked from commit bf410c6eda515364db5f6ed74b765efdec0595ae)