private void removeUsernameFromSizeCache(String username) {
        // Update the cached size if it exists.
        sizeCache.remove(username);
    }
Deletes all offline messages in the store for a user.

@param username the username of the user who's messages are going to be deleted.
xmppserver/src/main/java/org/jivesoftware/openfire/OfflineMessageStore.java