Remove VARIABLE_SUBSTITUTION table from the database

Issue Summary

When Bamboo is upgraded from old version before 5.x, entries in the table VARIABLE_SUBSTITUTION are migrated to a different table. However, the table and its values remaining uncleaned. This results in some sensitive variable values appearing unencrypted in the database.

Expected Results

The table must be deleted or the contents in it must be cleared.

Actual Results

The old entries remain intact in the table; thereby resulting in displaying some sensitive old variable values in plaintext.

Workaround

Manually delete the contents of this table.