Remove reading of symbols from a.out loaded files. Since we are tight
on space for clang and a.out support is only needed for /boot/loader,
they are excess bytes that serve no useful purpose other than to
support really old kernels (FreeBSD < 3.2 or so). Prefer clang
support over support for these old kernels and remove this code. We
gain about 100 bytes of space this way.

Reviewed by: rdivacky@