apps: createsamples: fix comment to remove last backslash

[Kumataro]

Close #25403

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
• [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable Patch to opencv_extra has the same branch name.
• [ ] The feature is well documented and sample code can be built with the project CMake

[Kumataro]

createsamples application had been disabled a few years ago. To test, this patch enables it temporary . If passed, I wll revert it to disable it.

[Kumataro]

Test is passed, so I revert to disable createsamples application again.