How to reproduce:
1. Open the attached project (it has .java plugin)
2. In Build Settings enable "Export Project" and keep Symlink Sources off
3. Export project and specify folder where you want it to be exported
3.1 Examine exported project MyExportedProject/unityLibrary/src/java/com
3.2 Notice that it has unity/statictestj folder with JavaPlug.java
4. Go back to Unity and set Symlink Sources on in Build Settings
5. Export project to the same folder where it was exported in Step 3

Actual result: unity/statictestj folder with JavaPlug.java remains in the project and building project via Android Studio fails because of
duplicate class: com.unity.statictestj.JavaPlug
Expected result: When exporting on top of another project, files which are not needed should be deleted.

Reproduced: 2021.2.0a2, 2020.2.0b13, 2019.4.18f1