Proposal: drop ldconfig from /rescue

[coypu%sdf.org@localhost]

ldconfig in netbsd is purely for a.out support.
I don't think a.out support is important in /rescue, no platform we have
uses it (since long ago).

it's the majority of the machine-dependent logic in /rescue.
I'd like to remove ldconfig and mark it machine-independent obsolete.

I will commit this change in a few days if nobody objects.

(I don't see why anyone would, but I feel compelled to make a post for
a removal.)