Do not display purse when prize money is 0

[SathyaJayabal]

Challenge listings: when prize money is 0, do not display purse.
https://www.topcoder.com/challenges?bucket=openForRegistration&filter[tracks][data_science]=true
https://beta-community-app.topcoder.com/challenges?bucket=openForRegistration&filter[tracks][data_science]=true