Sure, you can do it. It'll leave a ring/gap between the hole in the frame and the shaft of the left side decocker.
How much dirt/dust/lint will work it's way into the frame through that hole? Who knows. Keep it cleaned/lubed on a regular basis and it probably won't be an issue.
I didn't watch the whole video. Did he say why he removed it?
My CZ's came with ambidextrous safeties (I'm not a decocker guy) so they were ready to go. When I carried a 1911 I installed ambidextrous safeties on them. I might not ever need to operate the pistol left handed, but ambidextrous controls make it much easier. Like having a spare magazine for my EDC gun. Hopefully 13 rounds of .40 S&W will be more than enough, but I still carry 17 more in the spare magazine in my pocket.