fix(s2n-quic-transport): revert "improve amplification credits on client #1818"

[WesleyRosenblum]

Description of changes:

In #1818 we made two changes to improve the success of handshakes succeeding in the face of packet loss and amplification limits on the server.

These two changes were:

1. Pad all datagrams transmitted by the client until the handshake has been confirmed, regardless of whether an initial packet was included in the datagram
2. Force all packets transmitted during the handshake to be ack-eliciting by including a Ping frame in the packet

1. Should not be necessary since receipt of a Handshake packet on the server removes amplification limits, so padding a solitary Handshake packet would only serve to give amplification credits that would no longer be needed. From QUIC§8,1:

Connection establishment implicitly provides address validation for both endpoints. In particular, receipt of a packet protected with Handshake keys confirms that the peer successfully processed an Initial packet. Once an endpoint has successfully processed a Handshake packet from the peer, it can consider the peer address to have been validated.

2. Is addressed by #1894, which arms the PTO timer for the handshake regardless of whether the handshake space has any transmission to send (ack-eliciting or otherwise). All PTO probes are ack-eliciting.

Testing:

Will verify in Interop

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