Tidy up the docstring of Widget._scroll_to

Delivering on a promise made in Textualize#1920.

src/textual/widget.py

@@ -1442,7 +1442,7 @@ def _scroll_to(
             speed: Speed of scroll if `animate` is `True`. Or `None` to use duration.
             duration: Duration of animation, if `animate` is `True` and speed is `None`.
             easing: An easing method for the scrolling animation.
-            force: Force scrolling even when prohibited by overflow styling. Defaults to `False`.
+            force: Force scrolling even when prohibited by overflow styling.
 
         Returns:
             `True` if the scroll position changed, otherwise `False`.