Removal of $PGDATA/base files that existed before streaming replication (v9.2.4)

I set up streaming replication using the rsync base backup described in the wiki: http://wiki.postgresql.org/wiki/Binary_Replication_Tutorial

However, before starting replication I had previously loaded some databases on the "Secondary" server for testing. Folders for those db's are still in base/ and are consuming a lot of disk space. du reports that the base on my Secondary is twice as large as on the Primary. 

Do I have safe options for removing this unused data, beyond clearing the Secondary's $PGDATA folder and re-doing the synchronization?

Cheers,
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