http2: no stream destroy while its data is on the wire

This fixes a crash that occurred when a `Http2Stream` write
is completed after it is already destroyed.

Instead, don’t destroy the stream in that case and wait for
GC to take over.

PR-URL: https://github.com/nodejs/node/pull/19002
Fixes: https://github.com/nodejs/node/issues/18973


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>