Stop updating problem_version and set_version tables for the admin course.

These are virtual tables and therefore not native.  The admin course updates non-native tables (ones that are global for all courses, not defined on a course by course basis) but these virtual tables do not need to be updated.

This is a hack.  If more virtual tables are created this fix will have to
be updated.

To check this you can use mysql commands to delete the version_id field from
problem_user table of the admin course.  Without this upgrade that version_id field will always be added back.  With this upgrade the version_id field, once deleted, will stay deleted from the database.

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Merge pull request #400 from mgage/fix_admin_database

Fix admin database

I deleted version_id from both admin_user_set and admin_user_problem and it was not added by the admin course and there was no error.