Revert "Update Challenge.java (#117)"

This reverts acbf332.

src/main/java/com/bytelegend/Challenge.java

@@ -20,16 +20,6 @@ public static void main(String[] args) {
      * <p>If there is no root, return an empty array.
      */
     public static double[] calculate(int a, int b, int c) {
-        double delta = b * b - 4 * a * c;
-        if (delta < 0) {
-            return new double[] {};
-        } else if (delta == 0) {
-            double root = -b / (2.0 * a);
-            return new double[] {root};
-        } else {
-            double root1 = (-b + Math.sqrt(delta)) / (2.0 * a);
-            double root2 = (-b - Math.sqrt(delta)) / (2.0 * a);
-            return new double[] {root1, root2};
-        }
+        return null;
     }
 }