These are old feature flags that are no longer used:
ENABLE_MANUAL_GIT_RELOAD was to allow instructors to reload an XML
Modulestore course directly from a git checkout. That Modulestore
backend hasn't existed for a while.
DEBUG_LEVEL was an early flag for how debug log verbosity.
USE_YOUTUBE_OBJECT_API was created in reaction to YouTube breaking
their iframe API. They have long since addressed those issues.