[css-fonts-4] Remove redundant grammar

Remove redundant <angle> in the font-style @font-face descriptor.

Author: xfq

css-fonts-4/Overview.bs

@@ -2449,7 +2449,7 @@ Font property descriptors: the 'font-style!!descriptor', 'font-weight!!descripto
 
 	<pre class='descdef'>
 	Name: font-style
-	Value: auto | normal | italic | oblique [ <<angle>> | <<angle>>{1,2} ]?
+	Value: auto | normal | italic | oblique [ <<angle>>{1,2} ]?
 	For: @font-face
 	Initial: auto
 	</pre>