RedirectMatch is a mod_alias directive, so the "RewriteEngine On" directive does nothing here.
However, I believe that the function that you need to clear the query string may require the use of mod_rewrite, so let's replace the RedirectMatch instead of removing the RewriteEngine directive:
RewriteRule ^.*$ http://new-example.co[b]m/?[/b] [R=301,L]