EigValsh and calc_eigenvec

I noticed that the `calc_eigenvec` parameter is set to true, even if only the eigenvalues are requested (see [here](https://github.com/rust-ndarray/ndarray-linalg/blob/34f7b998eab0276bbd27fb752258f838a4bc1778/ndarray-linalg/src/eigh.rs#L192)). Is there a reason for this? The calculation should probably much faster without that.