prep: Remove bogus BIOS size check

r3480 added this check to account for the entry vector 0xfff00100 to be
available for CPUs that need it. Today however, the NIP is not yet
initialized at this point (zero), so the check always triggers.

Moreover, BIOS size check is already done previously, so this part can
be removed too.

Cc: Alexander Graf <agraf@suse.de>
Signed-off-by: Andreas Färber <andreas.faerber@web.de>
Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
