Merge pull request #24980 from fengyuentau:on-fly-quantization-removal

dnn cleanup: On-fly-quantization removal #2498

On-fly-quantization is first introduced via https://github.com/opencv/opencv/pull/20228.
We decided to remove it but keep int8 layers implementation because on-fly-quantization
is less practical given the fact that there has been so many dedicated tools for model
quantization.

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/test/test_int8_layers.cpp

@@ -2,6 +2,10 @@
 // It is subject to the license terms in the LICENSE file found in the top-level directory
 // of this distribution and at http://opencv.org/license.html.
 
+// The tests are disabled, because on-fly quantization was removed in https://github.com/opencv/opencv/pull/24980
+// To be restored, when test models are quantized outsize of OpenCV
+#if 0
+
 #include "test_precomp.hpp"
 #include "npy_blob.hpp"
 #include <opencv2/dnn/shape_utils.hpp>
@@ -1389,3 +1393,5 @@ TEST_P(Test_Int8_nets, YOLOv4_tiny)
 INSTANTIATE_TEST_CASE_P(/**/, Test_Int8_nets, dnnBackendsAndTargetsInt8());
 
 }} // namespace
+
+#endif // #if 0