refactor: move xmodule folder to root

- Moving xmodule folder to root as we're dissolving sub-projects of common folder in edx-platform
    - More info: https://openedx.atlassian.net/browse/BOM-2579
- -e common/lib/xmodule has been removed from the requirements as xmodule has itself become the part of edx-platform and not being installed through requirements
- The test files common/lib/xmodule/test_files/ have been removed as they are not being used anymore

webpack-config/file-lists.js

@@ -12,7 +12,7 @@ module.exports = {
         path.resolve(__dirname, '../common/static/common/js/components/utils/view_utils.js'),
         /descriptors\/js/,
         /modules\/js/,
-        /common\/lib\/xmodule\/xmodule\/js\/src\//,
+        /xmodule\/js\/src\//,
         path.resolve(__dirname, '../openedx/features/course_bookmarks/static/course_bookmarks/js/views/bookmark_button.js')
     ],