Apparently you still have leftover files referencing the old plugin before it was merged into OculusVR. To fix, delete these folders:
Saved/Cooked
Saved/StagedBuilds
Intermediate/Build
Your editor will need to recompile all the shaders, but if you were to copy stuff to a new project, that would also happen, so there’s no loss here.
Also, if you already launched your project on Android, you might have to delete the cache on your phone, located at
/sdcard/UE4Game/YourGame/