[css-position-3] Fix markup

Author: fantasai

css-position-3/Overview.bs

@@ -450,7 +450,7 @@ Box Insets: the 'top', 'right', 'bottom', 'left', 'inset-block-start', 'inset-in
 	These [=inset properties=] represent an inward “inset”
 	on the corresponding side of the box
 	(with respect to the box’s own [=writing mode=];
-	see [[!CSS-WRITING-MODES-3#abstract-box]]).
+	see [[CSS-WRITING-MODES-3#abstract-box]]).
 	For example, 'top' represents a downward inset of the top edge.
 	The [=physical=] and [=flow-relative=] properties
 	interact as defined in [[!CSS-LOGICAL-1]].