Removes the heuropt-plot subcrate, the visualize example that used
it, and the related workspace plumbing (root [workspace] table, the
[workspace] override added to fuzz/Cargo.toml to detach from it,
heuropt-plot dev-dep, CHANGELOG mention).
The visualization concern is better served as an independent third-
party project than as a companion crate in this repo. No effect on
heuropt's public API or the async work in 0.8.0.
swaits
af226e3d3b