You need two rules. In some cases there will be a double redirection tho.
<IfModule mod_rewrite.c>
RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
RewriteRule ^ https://%1%{REQUEST_URI} [R=301,L]
RewriteCond %{SERVER_PORT} !^443
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
</IfModule>
Edit: now it will remove the www part.
Please note that your SSL cert does only match site.com but not www.site.com, which will cause security alerts when you access it via https://www
, I'm not sure you can avoid that with htaccess rules.
The first rule will trigger and redirect https:// + www
to https:// without www
, but the alert might fire anyway. Just give it a try.