Remove thread id from ThreadWrapper::Start().

Removes ThreadPosix::InitParams and a corresponding wait for an event.
This unblocks ThreadPosix::Start which had to wait for thread scheduling
for an event to trigger on the spawned thread, giving faster Start()
calls.

BUG=4413
R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/43699004

Cr-Commit-Position: refs/heads/master@{#8709}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8709 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/audio_coding/main/test/APITest.cc

@@ -38,8 +38,7 @@ namespace webrtc {
 #define MAX_FILE_NAME_LENGTH_BYTE 500
 #define CHECK_THREAD_NULLITY(myThread, S)                                      \
   if(myThread != NULL) {                                                       \
-    unsigned int i;                                                            \
-    (myThread)->Start(i);                                                      \
+    (myThread)->Start();                                                       \
   } else {                                                                     \
     ADD_FAILURE() << S;                                                        \
   }