Remove objc_sync_enter/objc_sync_exit

[hamin]

I think we should just be able to use dispatch lock queues here like so:

let lockQueue = dispatch_queue_create("com.test.LockQueue", nil)
dispatch_sync(lockQueue) {
    // code
}

/cc @shams-ahmed

[shams-ahmed]

@hamin I agree only used objc_sync_enter due to its easy of use. ones the projects moved to swift 3 dispatch queue should be the way forward

[fengshi92]

May I ask when will this issue be addressed? It sometimes causes my urlSession delegate queue deadlock. Looking forward to hear from you!

[hamin]

@fengshi92 i haven't had a chance to look at this yet. Do you wanna take a shot at it and submit a PR? Since you're experiencing a deadlock issue right now your input would be super valuable

[fengshi92]

Due to legal reason of my company, I can't submit a pull request right now. Maybe later I could submit a fix. However I just want to let you know that the proposed method above resolved my problem. Thanks!

[hamin]

fixed by #27