docs(Overlay): fix double word typo (#6569)

www/src/pages/components/overlays.mdx

@@ -156,7 +156,7 @@ Since we can't know every time your overlay changes size, to reposition
 it, you need to take manual action if you want to update the position of
 an Overlay in response to a change.
 
-For this, the Overlay component also injects a a `popper`
+For this, the Overlay component also injects a `popper`
 prop with a `scheduleUpdate()` method that an overlay
 component can use to reposition itself.