Remove parent.start() from CancellableContinuationImpl.kt (Kotlin#2036)

It seems to be the legacy from times when CC was a Job, in order to observe behaviour change, a specific example should be accurately made

Author: qwwdfsad

kotlinx-coroutines-core/common/src/CancellableContinuationImpl.kt

@@ -114,7 +114,6 @@ internal open class CancellableContinuationImpl<in T>(
         if (checkCompleted()) return
         if (parentHandle !== null) return // fast path 2 -- was already initialized
         val parent = delegate.context[Job] ?: return // fast path 3 -- don't do anything without parent
-        parent.start() // make sure the parent is started
         val handle = parent.invokeOnCompletion(
             onCancelling = true,
             handler = ChildContinuation(parent, this).asHandler