Auto merge of #2068 - Minoru:bugfix/remove-unused-iconv.h, r=JohnTitor
Auto merge of #2068 - Minoru:bugfix/remove-unused-iconv.h, r=JohnTitor

Remove unused iconv.h includes

These are left over from 3e4d684dcdd1dff363a45c70c914204013810155, which
added includes to *all* platforms despite adding bindings only to *some*
of them. This already broke OpenBSD which doesn't have iconv.h (fixed by
915d8fac81f40b7f2622523725634d049acff6ea), and is just distasteful, so
down with those unused includes.

(This is a continuation to #2037 and #2067.)

rust-lang/libc,rust-lang/libc,rust-lang/libc