Deletes Acount points starting at position Index.
xyzArray a = new xyArray(4);
a[0]= new xyz(1, 1);
a[1]= new xyz(1,-1);
a[2]= new xyz(3, 4);
a[3]= new xyz(2, 2);
a.delete(1, 2);
//now a has count = 2;
// a[0] = (1, 1);
// a[1] = (2, 2);
//