Fix shorthand `legend: false` and `title: false`

Fix shorthand `legend: false` and `title: false`

Prevent attempt to remove the legend or title layout items if they haven't been created but also check if the item to remove is registered with the layout manager to avoid removing the wrong box `splice(-1, 1)`. Add ids to the legend and title plugins to allow to fully disable them (`options: {plugins: {legend: false, title: false}}`).