Remove duplicate calculation of output shape (pytorch#26684)

Summary:
Pull Request resolved: pytorch#26684

Output heights and widths are already calculated by conv_p. Remove the duplicate calculation.
ghstack-source-id: 90633432

Test Plan:
buck test mode/dev caffe2/test:quantized
```
Summary (total time 18.69s):
  PASS: 45
  FAIL: 0
  SKIP: 10
    caffe2/test:quantized - test_qadd_scalar_relu (test_quantized.TestQuantizedOps)
    caffe2/test:quantized - test_equal (test_quantized.TestQuantizedOps)
    caffe2/test:quantized - test_qnnpack_add (test_quantized.TestQNNPackOps)
    caffe2/test:quantized - test_qconv_unpack (test_quantized.TestQNNPackOps)
    caffe2/test:quantized - test_qlinear_unpack (test_quantized.TestQNNPackOps)
    caffe2/test:quantized - test_compare_tensor_scalar (test_quantized.TestComparatorOps)
    caffe2/test:quantized - test_qconv_qnnpack (test_quantized.TestQNNPackOps)
    caffe2/test:quantized - test_qlinear_qnnpack (test_quantized.TestQNNPackOps)
    caffe2/test:quantized - test_qnnpack_relu (test_quantized.TestQNNPackOps)
    caffe2/test:quantized - test_qnnpack_maxpoolMore details at https://our.intern.facebook.com/intern/buck/build/3b394f1e-ab99-4e59-bdf5-2766f46e9869
2d (test_quantized.TestQNNPackOps)
  FATAL: 0
  TIMEOUT: 0
  OMIT: 0
```

Differential Revision: D17538375

fbshipit-source-id: b4b60e93fdec4cc7bbf6aee7182381221dfac243

Author: dskhudia

aten/src/ATen/native/quantized/cpu/qconv.cpp

@@ -194,9 +194,9 @@ class QConv2dInt8 final : public c10::OperatorKernel {
       TORCH_CHECK(false, "[QConv2D] Unknown quantization scheme");
     }
 
-    // TODO: change convOutputShape to return NCHW sizes once perf is fixed
-    auto outShape =
-        convOutputShape(N, K, H, W, kernel, stride, padding, dilation);
+    // TODO: change the following to NCHW sizes once perf is fixed
+    SmallVector<int64_t, 4> outShape{
+        N, conv_p.OUT_DIM[0], conv_p.OUT_DIM[1], K};
     TORCH_CHECK(
         std::all_of(
             outShape.begin(), outShape.end(), [](int64_t i) { return i > 0; }),