Furthermore the CSS google is generating is using @font-face, which has a url in it as well. What I would do is go to the direct CSS that google is linking too, copy it, paste it into a separate CSS file, and import the path to the local CSS file you created for the @font-face. It's dirty, but a work around.
In order to improve compatibility with CSS it'd be useful if LESS would just pass such things on without touching it. The CSS files Google generates are browser-dependent and the URLs are an implementation detail that may change without advance notice, so trying to include them directly would be a bad idea.
LESS promises to be fully compatible with CSS, so dropping or choking is not an acceptable behaviour for CSS syntax.