remove use of deprecated `metaFields` option (#4073)

examples/svelte-example/src/App.svelte

@@ -8,7 +8,7 @@
 		return new Uppy().use(Webcam).use(XHRUpload, {
 			bundle: true,
 			endpoint: 'http://localhost:9967/upload',
-			metaFields: ['something'],
+			allowedMetaFields: ['something'],
 			fieldName: 'files',
 		})
 	}

examples/xhr-bundle/main.js

@@ -20,6 +20,6 @@ uppy.use(Dashboard, {
 uppy.use(XHRUpload, {
   bundle: true,
   endpoint: 'http://localhost:9967/upload',
-  metaFields: ['something'],
+  allowedMetaFields: ['something'],
   fieldName: 'files',
 })

website/src/docs/xhr-upload.md

@@ -261,7 +261,7 @@ By default, all metadata is sent, including Uppy’s default `name` and `type` m
 ```js
 uppy.use(XHRUpload, {
   // Only send our own `size` metadata field.
-  metaFields: ['size'],
+  allowedMetaFields: ['size'],
 })
 ```