x86: Remove a.out support

Commit

  eac61655 ("x86: Deprecate a.out support")

deprecated a.out support with the promise to remove it a couple of
releases later. That commit landed in v5.1.

Now it is more than a couple of releases later, no one has complained so
remove it.

Fold in a hunk removing the reference to arch/x86/ia32/ia32_aout.c in
MAINTAINERS:

  https://lore.kernel.org/r/20220316050828.17255-1-lukas.bulwahn@gmail.com



Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220113160115.5375-1-bp@alien8.de