SUNRPC: Remove dead code in svc_tcp_release_rqst()

[ Upstream commit 4af8b42e ]

Clean up: svc_tcp_sendto() always sets rq_xprt_ctxt to NULL.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Stable-dep-of: 948f072a ("SUNRPC: always free ctxt when freeing deferred request")
Signed-off-by: Sasha Levin <sashal@kernel.org>