Remove likely outdated warning.

Replacing '() => field.focus()' with '{field.focus}' doesn't throw an error.

If 'can't do `{field.focus}`' refers to reading that value in the HTML section of the file then there's earlier files where this warning should be placed.

site/content/tutorial/06-bindings/14-component-this/text.md

@@ -19,5 +19,3 @@ Now we can programmatically interact with this component using `field`.
 	Focus field
 </button>
 ```
-
-> Note that we can't do `{field.focus}` since field is undefined when the button is first rendered and throws an error.