bsd-user: Eliminate elf personality

The linux kernel supports a number of different ELF binaries. The Linux userland
emulator inheritted some of that. And we inheritted it from there. However, for
BSD there's only one kind of ELF file supported per platform, so there's no need
to cope with historical quirks. Simply the code as a result.

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>