Simplify shim timeout logic.

I don't think this lock is actually needed. If the process exited by the
time we call shim.Process.Kill(), then the test ultimately finished. If
not, wait() will return that the process died by a signal.

Change-Id: I668a86583aba16fd00e0cd05071acc13059a2c42
Reviewed-on: https://boringssl-review.googlesource.com/27325
Reviewed-by: Adam Langley <agl@google.com>

ssl/test/runner/runner.go

@@ -1210,21 +1210,11 @@ func runTest(test *testCase, shimPath string, mallocNumToFail int64) error {
 	if *useGDB {
 		childErr = <-waitChan
 	} else {
-		var shimKilledLock sync.Mutex
-		var shimKilled bool
 		waitTimeout := time.AfterFunc(*idleTimeout, func() {
-			shimKilledLock.Lock()
-			shimKilled = true
-			shimKilledLock.Unlock()
 			shim.Process.Kill()
 		})
 		childErr = <-waitChan
 		waitTimeout.Stop()
-		shimKilledLock.Lock()
-		if shimKilled && err == nil {
-			err = errors.New("timeout waiting for the shim to exit.")
-		}
-		shimKilledLock.Unlock()
 	}
 
 	var isValgrindError, mustFail bool