Remove unused assignment in db/db_iter.cc
Remove unused assignment in db/db_iter.cc

Summary:
"make analyze" complains the assignment is not useful. Remove it.
Closes https://github.com/facebook/rocksdb/pull/1581

Differential Revision: D4241697

Pulled By: siying

fbshipit-source-id: 178f67a

SunguckLee/RocksDB,Andymic/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,bbiao/rocksdb,bbiao/rocksdb,vmx/rocksdb,vmx/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,bbiao/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,wat-ze-hex/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,Andymic/rocksdb,bbiao/rocksdb,vmx/rocksdb,vmx/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,wat-ze-hex/rocksdb,vmx/rocksdb,vmx/rocksdb