9.2.0 tarball contains unrelated files

The v9.2.0 qemu tarballs (and -rcS too) contain a set of unrelated files which should not be there, - subprojects/packagecache/ contains all rust crates included, in .tar.gz form. This probably should be fixed in scripts/make-release.sh.

Another note is that rust crates which are included in source form, such as subprojects/proc-macro2-1.0.84/, contains Cargo.toml.orig files. I understand these are more special in rust/cargo world than regular foo.c.orig files sometimes created by patch utility. But it is still a bit confusing, - I dunno if these actually should be there or not. Again, it's something to decide in scripts/make-release.sh.

@bonzini @mdroth Can you take a look please? Obviously it's too late for 9.2.0 tarballs, but we can fix this in the future.