link studio startup.py to lms/startup.py

See Issue #2397

When custom themes are enabled and set, studio startup fails since it doesn't check or set theming paths (even as it may not use theming items).

This PR removes `cms/startup.py`, and links it to `lms/startup.py`.

Sort of related to PR #3094 (which enables theming configuration thru ansible).

@singingwolfboy - please review.