[css-round-display] Remove polar positioning intro

Author: xfq

css-round-display/Overview.bs

@@ -62,15 +62,12 @@ To apply the shape of a display to content area, we extend the 'shape-inside' pr
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 We also add the 'border-boundary' property to CSS Borders. The borders of the element can be drawn along the edge of the display even if the element is overflowed.
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-For the better web design suitable for a round display, we introduce polar positioning.
-In conventional positioning method, the Cartesian coordinates, elements are positioned by offsets in x-axis and y-axis. But, we suggest a method to position elements with specifying the distance and angle from the origin point of coordinates.
 
 This module provides features such as:
 
 	* 	Detecting the rounded display
 	* 	Aligning contents in the display’s shape
 	* 	Drawing borders along the display’s edge
-	* 	Positioning elements in polar coordinates
 
 Terminology {#terminology}
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