Remove FF_CONFIGURABLE_ROOT_DIR Feature Flag

What does this MR do?

This MR removes the FF_CONFIGURABLE_ROOT_DIR Feature Flag after it has been default-enabled for 4 months now with no issues.

TODO

• Feature flag
  • Added Removed feature flag: #1073 (closed)
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines