fix #2117; delete obsolete sentence

docs/marks/area.md

@@ -308,7 +308,7 @@ Plot.areaY(observations, {x: "date", y: "temperature", interval: "day"})
 
 The **interval** option is recommended to “regularize” sampled data; for example, if your data represents timestamped temperature measurements and you expect one sample per day, use "day" as the interval.
 
-The **areaY** mark draws the region between a baseline (*y1*) and a topline (*y2*) as in an area chart. When the baseline is *y* = 0, the *y* channel can be specified instead of *y1* and *y2*. For example, here is an area chart of Apple’s stock price.
+The **areaY** mark draws the region between a baseline (*y1*) and a topline (*y2*) as in an area chart. When the baseline is *y* = 0, the *y* channel can be specified instead of *y1* and *y2*.
 
 ## areaX(*data*, *options*) {#areaX}