If you remove the query string you’ll eventually still have the issue of a stale cache in the email editor. (You’ll note the editor styles are not applied to the actual email).
What you can do instead is append your own custom string when you need to bust the browser cache. Here’s a link to a stackexchange answer that has some example PHP code you can add to a plugin:
The support post ‘Remove CSS version numbers’ is closed to new replies.
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