linux-user: Remove partial support for a.out interpreters.

linux-user: Remove partial support for a.out interpreters.

At the bottom of the a.out support was the unimplemented load_aout_interp
function.  There were other portions of the support that didn't look
right; when I went to look in the Linux kernel for clarification, I found
that the support for such interpreters has been removed from binfmt_elf.
There doesn't seem to be any reason to keep this broken support in qemu.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>