No prefix iterator in db_stress
No prefix iterator in db_stress

Summary: We're trying to deprecate prefix iterators, so no need to test them in db_stress

Test Plan: ran it

Reviewers: ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16917

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cksdb,skunkwerks/rocksdb,RyanTech/rocksdb,NickCis/rocksdb,JohnPJenkins/rocksdb,wenduo/rocksdb,anagav/rocksdb,kaschaeffer/rocksdb,msb-at-yahoo/rocksdb,lgscofield/rocksdb,bbiao/rocksdb,Vaisman/rocksdb,tschottdorf/rocksdb,vmx/rocksdb,OverlordQ/rocksdb,makelivedotnet/rocksdb,vashstorm/rocksdb,flabby/rocksdb,IMCG/RcoksDB,siddhartharay007/rocksdb,RyanTech/rocksdb,makelivedotnet/rocksdb,facebook/rocksdb,vmx/rocksdb,Applied-Duality/rocksdb,OverlordQ/rocksdb,hobinyoon/rocksdb,JoeWoo/rocksdb,amyvmiwei/rocksdb,bbiao/rocksdb,tizzybec/rocksdb,SunguckLee/RocksDB,virtdb/rocksdb,caijieming-baidu/rocksdb,facebook/rocksdb,msb-at-yahoo/rocksdb,bbiao/rocksdb,luckywhu/rocksdb,hobinyoon/rocksdb,mbarbon/rocksdb,JohnPJenkins/rocksdb,tschottdorf/rocksdb,temicai/rocksdb,rDSN-Projects/rocksdb.replicated,biddyweb/rocksdb,IMCG/RcoksDB,tizzybec/rocksdb,siddhartharay007/rocksdb,Andymic/rocksdb,wenduo/rocksdb,ylong/rocksdb,OverlordQ/rocksdb,siddhartharay007/rocksdb,mbarbon/rocksdb,alihalabyah/rocksdb,wenduo/rocksdb,ryneli/rocksdb,wskplho/rocksdb,Andymic/rocksdb,bbiao/rocksdb,jalexanderqed/rocksdb,vashstorm/rocksdb,facebook/rocksdb,amyvmiwei/rocksdb,Andymic/rocksdb,dkorolev/rocksdb,ylong/rocksdb,fengshao0907/rocksdb,lgscofield/rocksdb,bbiao/rocksdb,dkorolev/rocksdb,makelivedotnet/rocksdb,vashstorm/rocksdb,ryneli/rocksdb