Remove duplicated code for clarity

Author: MisaOgura

intro-neural-networks/gradient-descent/GradientDescent.ipynb

@@ -141,8 +141,6 @@
     "    for e in range(epochs):\n",
     "        del_w = np.zeros(weights.shape)\n",
     "        for x, y in zip(features, targets):\n",
-    "            output = output_formula(x, weights, bias)\n",
-    "            error = error_formula(y, output)\n",
     "            weights, bias = update_weights(x, y, weights, bias, learnrate)\n",
     "        \n",
     "        # Printing out the log-loss error on the training set\n",