This should improve performance for courseware operations when there is
content that doesn't map to any existing XBlocks in the system. This
usually happens to old courses when custom XBlock types are deprecated
and removed, or when a course is imported from another instance with a
different set of installed XBlocks.
- 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
