Only call DiscoveryStopped once when discovery stops

The call to BluetoothTaskManagerWin::DiscoverDevices runs on a loop
until either discovery stops or we find the device we are searching for.
If discovery stops this function called
BluetoothTaskManagerWin::OnStopDiscovery.  However, we call
BluetoothTaskManagerWin::OnStopDiscovery already when we stop. The
second call causes a crash. This CL removes that call.

Bug: 1022149
Change-Id: I74d977abdfd69cbde2e525a024b1f6016148ed7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1915300Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715843}

device/bluetooth/bluetooth_task_manager_win.cc

@@ -455,12 +455,8 @@ void BluetoothTaskManagerWin::StopDiscovery() {
 
 void BluetoothTaskManagerWin::DiscoverDevices(int timeout_multiplier) {
   DCHECK(bluetooth_task_runner_->RunsTasksInCurrentSequence());
-  if (!discovering_ || !classic_wrapper_->HasHandle()) {
-    ui_task_runner_->PostTask(
-        FROM_HERE,
-        base::BindOnce(&BluetoothTaskManagerWin::OnDiscoveryStopped, this));
+  if (!discovering_ || !classic_wrapper_->HasHandle())
     return;
-  }
 
   std::vector<std::unique_ptr<DeviceState>> device_list;
   if (SearchDevices(timeout_multiplier, false, &device_list)) {