util: BufferPool: removes unused fields
util: BufferPool: removes unused fields

hustbill/goleveldb,btcsuite/goleveldb,no2key/goleveldb,conseweb/goleveldb,rentongzhang/goleveldb,ngaut/goleveldb,syndtr/goleveldb,trigrass2/goleveldb,zzl0/goleveldb,FactomProject/goleveldb,chai2010/goleveldb