They're jettisoning the RSA key transport handshake; that is, the part of the protocol where a client generates a session secret all by themselves, encrypts it with the server's RSA key, and sends the RSA-encrypted blob to the server.

The forward-secret handshake uses Diffie Hellman (or, more commonly, ECDH) so that both sides of the connection cooperate to derive the session secret. RSA is still used in the forward-secret handshake, but only to sign the DH handshake, to protect it from MITM attackers.