Remove unused bar property and confusing docs referring to it (#7333)

docs/docs/developers/charts.md

@@ -114,6 +114,3 @@ new Chart(ctx, {
     options: options
 });
 ```
-
-### Bar Controller
-The bar controller has a special property that you should be aware of. To correctly calculate the width of a bar, the controller must determine the number of datasets that map to bars. To do this, the bar controller attaches a property `bar` to the dataset during initialization. If you are creating a replacement or updated bar controller, you should do the same. This will ensure that charts with regular bars and your new derived bars will work seamlessly.

docs/docs/getting-started/v3-migration.md

@@ -197,8 +197,9 @@ The following properties and methods were removed:
 * `Chart.Tooltip` is now provided by the tooltip plugin. The positioners can be accessed from `tooltipPlugin.positioners`
 * `ILayoutItem.minSize`
 
-#### Dataset Controller
+#### Dataset Controllers
 
+* `BarController.getDatasetMeta().bar`
 * `DatasetController.addElementAndReset`
 * `DatasetController.createMetaData`
 * `DatasetController.createMetaDataset`

src/controllers/controller.bar.js

@@ -246,7 +246,6 @@ export default class BarController extends DatasetController {
 
 		const meta = me._cachedMeta;
 		meta.stack = me.getDataset().stack;
-		meta.bar = true;
 	}
 
 	update(mode) {