Good question. Wondered this myself. If I'm on a SID and that phrase is uttered by ATC, that to me means that the speed restrictions on the SID are no longer applicable- and I have yet to have a controller yell at me for exceeding the SID speed limits. However, I usually ask to exceed 250K below 10,000, even if they previously told me "speed restrictions removed" or "no speed restrictions."
I'd also want to know where it is written. I suspect we'll get answers like mine above, but what I would like to find the place to find such information for Vietnam, Hong Kong, Beijing, etc., etc., because the phrase may have different meetings in different countries.