remove ad from preview, closes https://github.com/MartijnR/enketo/issues/308
remove ad from preview, closes https://github.com/MartijnR/enketo/issues/308

ICT4H/dcs-web-enketo-core,mangroveorg/enketo-core-dw,alxndrsn/enketo-core,ICT4H/dcs-enketo-core,medic/enketo-core,nap2000/enketo-core,kevinmwangi/enketo-core,kevinmwangi/enketo-core,enketo/enketo-core,medic/enketo-core,kobotoolbox/enketo-core,yogeshsr/enketo-dw-clone,enketo/enketo-core,nap2000/enketo-core,mangroveorg/enketo-core-dw,enketo/enketo-core,alxndrsn/enketo-core,ICT4H/dcs-web-enketo-core,kobotoolbox/enketo-core,yogeshsr/enketo-dw-clone,nap2000/enketo-core,ICT4H/dcs-enketo-core