stand: Remove unused i386 EFI MD bits

r328169 removed the copy of bootinfo that would've made this somewhat
functional. However, this is irrelevant- earlier work in r292338 was done to
exit boot services in the MI bi_load() rather than having N copies of the
GetMemoryMap/ExitBootServices dance.

i386 never quite caught up to that; ldr_enter was still being called but
the prereq for that, ldr_bootinfo, was no longer. As a consequence, this
ExitBootServices() was being called with a mapkey=0, clearly bogus, and
reportedly breaking the boot in some instances.

Reported by: bcran
MFC after: 1 week