MenuItem aria-label just repeats the visible text

[afercia]

Noticed while looking at #12309

The MenuItem component has an aria-label attribute that just repeats the visible text of the menu item. For example:

<button type="button" aria-label="Visual Editor" aria-checked="true" role="menuitemradio" class="...">
    Visual Editor
</button>

While it doesn't harm anything, it's redundant. Not sure if there's a specific reason for the aria-label but, unless I'm missing something, maybe it could be simply removed?

[timwright12]

I can knock this one out today (via @10up)