Pass raw pointer of socket to QuicChromiumPacketWriter::OnSocketClosed

After https://chromium-review.googlesource.com/c/chromium/src/+/4570128,
when the connection closes, all of the sockets are deleted. Instead
of using std::move(), this CL passes the socket pointer as a raw
pointer instead of unique pointer so that we do not lose ownership
of the socket pointer in QuicChromiumClientSession::OnConnectionClosed.

Bug: 1465889
Change-Id: I970c846e1c657dcd2ca6ec0979fb728eb7643076
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4719085
Commit-Queue: Nidhi Jaju <nidhijaju@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1175280}