Remove exception for Initial padding

Builds on #2520.

Closes #2522.

draft-ietf-quic-transport.md

@@ -1469,10 +1469,9 @@ addresses.  In determining this limit, servers only count the size of
 successfully processed packets.
 
 Clients MUST ensure that UDP datagrams containing Initial packets are sized to
-at least 1200 bytes, padding packets in the datagram if necessary.  Once a
-client has received an acknowledgment for a Handshake packet it MAY send smaller
-datagrams.  Sending padded datagrams ensures that the server is not overly
-constrained by the amplification restriction.
+at least 1200 bytes, padding packets in the datagram if necessary.  Sending
+padded datagrams ensures that the server is not overly constrained by the
+amplification restriction.
 
 Packet loss, in particular loss of a Handshake packet from the server, can cause
 a situation in which the server cannot send when the client has no data to send