v2.0: Remove explicit stream finish (backport of #2760)

[mergify]

Problem

stream finish is redundant as StreamDrop is already doing that.
Removing that will allow next call to be made faster without waiting for the stream to be finished.

Summary of Changes

removed explicit stream finish

Fixes #

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This is an automatic backport of pull request #2760 done by [Mergify](https://mergify.com).

[alessandrod]

I want to backport this because it makes a big difference when sending txs over the internet (RTT not close to 0). Before the patch we were essentially serializing all tx writes, waiting for the server to ack one by one. Testing on a connection from US to korea, removing this line makes the difference between sending < 10 TPS to sending tens of thousands TPS.

The patch is safe, dropping the stream calls finish() internally anyway: https://github.com/quinn-rs/quinn/blob/3bd6f93a284a57ce551ddf2e77bb4233d568a34e/quinn/src/send_stream.rs#L276

Since QUIC guarantees delivery, even not calling finish we still get guaranteed delivery, from https://github.com/quinn-rs/quinn/blob/3bd6f93a284a57ce551ddf2e77bb4233d568a34e/quinn/src/send_stream.rs#L18

/// A stream that can only be used to send data
///
/// If dropped, streams that haven't been explicitly [`reset()`] will continue to (re)transmit
/// previously written data until it has been fully acknowledged or the connection is closed.

tldr: the patch is a big improvement and comes with no risk.

[t-nelson]

we like the red lines