iOS simulator showing a bar at the bottom in my horizontally-view game
In fact your assumption that there is a 'problem' is incorrect. This has nothing to do with your code, nor does the line represent the real-life microphone.
The black line you describe is displayed at the bottom of the screen by iOS to users to indicate they can swipe up from there.
This line can be either black or white, depending on what else is being displayed on the screen. The iOS Simulator is accurately simulating what will be seen by users on an actual hardware device.