LP#1667221: (follow-up) remove comment that is now a lie

LP#1667221: (follow-up) remove comment that is now a lie

Also, here's a test plan:

[1] Edit /openils/conf/oils_sip.xml and set the currency
    defined in the implementation section to be something
    other than USD.
[2] Start the SIP server and perform a patron information
    request; note that the BH field in the response contains
    'USD'.
[3] Apply the patch and restart the SIP server.
[4] Repeat step 2; this time, the currency should be whatever
    is specified in oils_sip.xml.
[5] Comment out the currency section in oils_sip.xml and restart
    the SIP server.
[6] Repeat step 2; this time, the currency should be back to 'USD'.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>