Let me give a clear answer.
You can make your own skin (or just edit an exisiting one) with blank countdown files. These would be count1.png, count2.png, count3.png, go.png, and ready.png. Then, you would need blank wav files for count1s.wav, count2s.wav, count3s.wav, gos.wav, and readys.wav.
The only time that this won't work is when a map has its own custom skin with a countdown. You can manually remove those for the time being, but once osz2 comes out, you won't be able to do workarounds like this.
So, since the majority of beatmaps don't have custom countdowns, you can "remove" the majority of countdowns with this method (although it's still not recommended since the countdown is there for a reason).