Merge pull request #22672 from ramasilveyra:docs/remove-dup-v4

* docs: remove duplicated step in Build .js doc

* docs: add missing emcmake prefix to command

doc/js_tutorials/js_setup/js_setup/js_setup.markdown

@@ -135,14 +135,7 @@ Building OpenCV.js from Source
 
     For example:
     @code{.bash}
-    python ./platforms/js/build_js.py build_js --cmake_option="-DOPENCV_EXTRA_MODULES_PATH=opencv_contrib/modules"
-    @endcode
-
--#  [optional] To enable OpenCV contrib modules append `--cmake_option="-DOPENCV_EXTRA_MODULES_PATH=/path/to/opencv_contrib/modules/"`
-
-    For example:
-    @code{.bash}
-    python ./platforms/js/build_js.py build_js --cmake_option="-DOPENCV_EXTRA_MODULES_PATH=opencv_contrib/modules"
+    emcmake python ./platforms/js/build_js.py build_js --cmake_option="-DOPENCV_EXTRA_MODULES_PATH=opencv_contrib/modules"
     @endcode
 
 -#  [optional] To enable WebNN backend, append `--webnn` option.