uefi(8): loader.efi does not search for loader.efi

This man page formerly referred to boot1.efi searching for loader.efi;
when boot1.efi was obsoleted in favour of having loader.efi launched
directly, this was left claiming that loader.efi searched for
loader.efi.

Reviewed by: bcran
Fixes: db8b56134506 Rework UEFI ESP generation
Differential Revision: https://reviews.freebsd.org/D32334

(cherry picked from commit 6fa58bfb3ecfad4aece948fd7e6a8ca3d60a18c2)