hgweb: remove unused Graph.cur property

hgweb: remove unused Graph.cur property

It was introduced in 0dba955c2636, but was already unused. I missed it in
e46f0b653002.

--- a/mercurial/templates/static/mercurial.js	Tue Dec 05 16:58:00 2017 -0500
+++ b/mercurial/templates/static/mercurial.js	Wed Dec 06 11:59:19 2017 +0800
@@ -29,7 +29,6 @@
 	this.ctx = this.canvas.getContext('2d');
 	this.ctx.strokeStyle = 'rgb(0, 0, 0)';
 	this.ctx.fillStyle = 'rgb(0, 0, 0)';
-	this.cur = [0, 0];
 	this.bg = [0, 4];
 	this.cell = [2, 0];
 	this.columns = 0;