dev-util/mingw64-runtime: revert "enable USE=libraries by default"

dev-util/mingw64-runtime: revert "enable USE=libraries by default"

This reverts commit 478d91086baa442fb578e0982063b93a19caf382.

Fresh bootstrap fails to build libraries as those need full stage2
compiler:

```
$ crossdev -t x86_64-w64-mingw32 -P -v

 * Emerging cross-mingw64-runtime ...
...
configure: error: in `.../mingw-w64-v6.0.0/mingw-w64-libraries/libmangle':
configure: error: C compiler cannot create executables
See `config.log' for more details
```

Disable default USE=libraries.

Reported-by: Rafael Kitover
Bug: https://bugs.gentoo.org/665512
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>