BSD.usr.dist: remove empty /usr/libdata/gcc directory

[mhorne]

Summary

I am unsure of its historical usage, but, we no longer ship GCC with
FreeBSD.

I note that I have several versions of gcc installed from ports, and
there is no /usr/local/libdata/gcc.

[emaste]

It came from rG:2bb58cb2e0c46298578b02d4448f69e4de166f16 and indeed is not used.
You could bump .Dd in hier.7 if you are so inclined.

[imp]

I think this is good. Maybe ask dim/jhb if there is some weird reason we need these?

[emaste]

We don't need these, they were just forgotten when GCC was removed.

ldscripts may be unused too.