uefi.8: update HISTORY and remove incomplete AUTHORS

• EFI support appeared in 5.0 for ia64
• arm64 UEFI support added in 11.0

The AUTHORS section included the folks responsible for the bulk of the
work to bring UEFI support to amd64, but missed those who did the
original work on ia64, the initial port to i386, the ports to arm64 and
arm, and have generally maintained and improved general UEFI support
since then. It's unwieldly to include everyone and would quickly become
outdated again anyhow, so just remove the AUTHORS section.

Reviewed by: manu
Discussed with: jhb
Differential Revision: https://reviews.freebsd.org/D14033