Removed useless locks in `distinct'
Removed useless locks in `distinct'

RxSwiftCommunity/RxSwiftExt,tgyhlsb/RxSwiftExt,RxSwiftCommunity/RxSwift-Ext,tgyhlsb/RxSwiftExt,RxSwiftCommunity/RxSwift-Ext,RxSwiftCommunity/RxSwiftExt,RxSwiftCommunity/RxSwiftExt