Removing destdir references from lang/rust

[Roland Illig <roland.illig%gmx.de@localhost>]

The package from lang/rust installs a few manifest files in lib/rustlib.
These manifest files refer to the temporary .destdir directory from
where the binary package was created.

Are these manifest files used for anything? I'm asking since none of the
paths mentioned in the manifest files actually exists. I suggest to
either remove the files or at least to remove the .destdir references
from them, but I'm not familiar with Rust, so I won't do that myself.

To reproduce this issue, build lang/rust with CHECK_WRKREF=destdir.