Clean up requirements.txt.
Clean up requirements.txt.

Delete unused code, don't comment it. That's what revision control is
for.

ErinCall/sync-engine,nylas/sync-engine,EthanBlackburn/sync-engine,Eagles2F/sync-engine,PriviPK/privipk-sync-engine,gale320/sync-engine,jobscore/sync-engine,rmasters/inbox,wakermahmud/sync-engine,nylas/sync-engine,closeio/nylas,jobscore/sync-engine,wakermahmud/sync-engine,wakermahmud/sync-engine,gale320/sync-engine,closeio/nylas,EthanBlackburn/sync-engine,rmasters/inbox,Eagles2F/sync-engine,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,ErinCall/sync-engine,gale320/sync-engine,ErinCall/sync-engine,PriviPK/privipk-sync-engine,ErinCall/sync-engine,wakermahmud/sync-engine,rmasters/inbox,EthanBlackburn/sync-engine,nylas/sync-engine,jobscore/sync-engine,closeio/nylas,PriviPK/privipk-sync-engine,Eagles2F/sync-engine,Eagles2F/sync-engine,gale320/sync-engine,nylas/sync-engine,EthanBlackburn/sync-engine,EthanBlackburn/sync-engine,Eagles2F/sync-engine,rmasters/inbox,jobscore/sync-engine,gale320/sync-engine,PriviPK/privipk-sync-engine,ErinCall/sync-engine,closeio/nylas