How to disable netdna.bootstrap.cdn

Hello,

I’ve been stuck on this for the last several days.

I’m optimizing my site for the speed. On several links during the load it waits for:
netdna.bootstrap.cdn

I check all php files of the theme and all plugin files, but was unable to find that css. When I view source of that link, it is right on the top, loading font awesome:
https://netdna.bootstrapcdn.com/font-awesome/4.3.0/css/font-awesome.css

How to disable loading of that css?

Because when I test the page with cleared cache sometimes it waits for more than 30 sec.

Thanks for any help.