[css-multicol] Remove redundant text

Closes w3c#1073

Author: frivoal

css-multicol/Overview.bs

@@ -941,8 +941,8 @@ Spanning columns</h2>
 		<dt><dfn>all</dfn>
 		<dd>
 			The element spans across all columns of the nearest multicol
-			ancestor in the same block formatting context. The element spans
-			across all columns. Content in the normal flow that appears before the
+			ancestor in the same block formatting context.
+			Content in the normal flow that appears before the
 			element is automatically balanced across all columns before the
 			element appears. The element establishes a new block formatting
 			context.