[Flow202][native][skip-ci] [6/x] Remove Scene type from ReactNav libdefs
Summary:
This type is not used anywhere and is not exported.
NOTE: CI will fail on this diff. I considered the possibility of fixing Flow errors BEFORE upgrading Flow, but it wasn't possible... in some cases, the fixes to support the new version of Flow caused errors in the old version. I could have hidden these type errors with $FlowFixMe lines and then later revert those, but that seemed like too much busy work.
Depends on D9989
Test Plan: Confirm the Flow errors go away
Reviewers: tomek
Reviewed By: tomek
Differential Revision: https://phab.comm.dev/D9990