Oracle Enterprise Manager Database Control is no longer used in 12c, so that a migration process to 12c drop the repository of Database Control. For this task Oracle includes the script /rdbms/admin/emremove.sql that performs the drop.
For the migration process it is necessary, but could be interesting in versions 11 or 10 to play or probe and after restoring the repository, tables, scheme, etc. Besides we want to do other tests.
HTH – Antonio NAVARRO