Delete pdf/epub artifacts when their build is disabled
Delete pdf/epub artifacts when their build is disabled

The reason for this is that old versions which had PDF builds in the past and
for which the PDF builds have been disabled will keep the stale PDF of old
builds lying around. We need to delete the artifacts if they exist and are
disabled for the current build.

Addresses https://github.com/rtfd/readthedocs.org/pull/1431#issuecomment-120998189

royalwang/readthedocs.org,kdkeyser/readthedocs.org,CedarLogic/readthedocs.org,kdkeyser/readthedocs.org,Tazer/readthedocs.org,clarkperkins/readthedocs.org,royalwang/readthedocs.org,royalwang/readthedocs.org,techtonik/readthedocs.org,asampat3090/readthedocs.org,wijerasa/readthedocs.org,GovReady/readthedocs.org,davidfischer/readthedocs.org,rtfd/readthedocs.org,CedarLogic/readthedocs.org,singingwolfboy/readthedocs.org,titiushko/readthedocs.org,michaelmcandrew/readthedocs.org,GovReady/readthedocs.org,kenshinthebattosai/readthedocs.org,wijerasa/readthedocs.org,tddv/readthedocs.org,rtfd/readthedocs.org,tddv/readthedocs.org,LukasBoersma/readthedocs.org,asampat3090/readthedocs.org,mhils/readthedocs.org,fujita-shintaro/readthedocs.org,wanghaven/readthedocs.org,kenshinthebattosai/readthedocs.org,attakei/readthedocs-oauth,emawind84/readthedocs.org,istresearch/readthedocs.org,gjtorikian/readthedocs.org,SteveViss/readthedocs.org,asampat3090/readthedocs.org,safwanrahman/readthedocs.org,gjtorikian/readthedocs.org,GovReady/readthedocs.org,SteveViss/readthedocs.org,VishvajitP/readthedocs.org,mhils/readthedocs.org,kenshinthebattosai/readthedocs.org,wijerasa/readthedocs.org,davidfischer/readthedocs.org,pombredanne/readthedocs.org,kenwang76/readthedocs.org,soulshake/readthedocs.org,emawind84/readthedocs.org,sunnyzwh/readthedocs.org,CedarLogic/readthedocs.org,michaelmcandrew/readthedocs.org,espdev/readthedocs.org,pombredanne/readthedocs.org,titiushko/readthedocs.org,istresearch/readthedocs.org,CedarLogic/readthedocs.org,espdev/readthedocs.org,sid-kap/readthedocs.org,laplaceliu/readthedocs.org,laplaceliu/readthedocs.org,LukasBoersma/readthedocs.org,VishvajitP/readthedocs.org,royalwang/readthedocs.org,techtonik/readthedocs.org,kenwang76/readthedocs.org,hach-que/readthedocs.org,emawind84/readthedocs.org,hach-que/readthedocs.org,gjtorikian/readthedocs.org,attakei/readthedocs-oauth,wijerasa/readthedocs.org,espdev/readthedocs.org,GovReady/readthedocs.org,atsuyim/readthedocs.org,michaelmcandrew/readthedocs.org,stevepiercy/readthedocs.org,istresearch/readthedocs.org,istresearch/readthedocs.org,sid-kap/readthedocs.org,SteveViss/readthedocs.org,rtfd/readthedocs.org,atsuyim/readthedocs.org,davidfischer/readthedocs.org,VishvajitP/readthedocs.org,davidfischer/readthedocs.org,Tazer/readthedocs.org,safwanrahman/readthedocs.org,safwanrahman/readthedocs.org,stevepiercy/readthedocs.org,attakei/readthedocs-oauth,pombredanne/readthedocs.org,espdev/readthedocs.org,mhils/readthedocs.org,titiushko/readthedocs.org,Tazer/readthedocs.org,michaelmcandrew/readthedocs.org,atsuyim/readthedocs.org,mhils/readthedocs.org,rtfd/readthedocs.org,titiushko/readthedocs.org,wanghaven/readthedocs.org,SteveViss/readthedocs.org,sid-kap/readthedocs.org,espdev/readthedocs.org,sunnyzwh/readthedocs.org,gjtorikian/readthedocs.org,VishvajitP/readthedocs.org,clarkperkins/readthedocs.org,hach-que/readthedocs.org,kenshinthebattosai/readthedocs.org,techtonik/readthedocs.org,laplaceliu/readthedocs.org,stevepiercy/readthedocs.org,fujita-shintaro/readthedocs.org,singingwolfboy/readthedocs.org,kdkeyser/readthedocs.org,laplaceliu/readthedocs.org,kdkeyser/readthedocs.org,soulshake/readthedocs.org,techtonik/readthedocs.org,asampat3090/readthedocs.org,emawind84/readthedocs.org,clarkperkins/readthedocs.org,LukasBoersma/readthedocs.org,tddv/readthedocs.org,Tazer/readthedocs.org,sunnyzwh/readthedocs.org,soulshake/readthedocs.org,sid-kap/readthedocs.org,hach-que/readthedocs.org,wanghaven/readthedocs.org,kenwang76/readthedocs.org,clarkperkins/readthedocs.org,wanghaven/readthedocs.org,soulshake/readthedocs.org,atsuyim/readthedocs.org,singingwolfboy/readthedocs.org,stevepiercy/readthedocs.org,singingwolfboy/readthedocs.org,fujita-shintaro/readthedocs.org,fujita-shintaro/readthedocs.org,LukasBoersma/readthedocs.org,sunnyzwh/readthedocs.org,safwanrahman/readthedocs.org,kenwang76/readthedocs.org,attakei/readthedocs-oauth