* guix-jupyter-kernel.scm (%notebook): Remove.
(reply-kernel-info-request): Remove 'socket' parameter; add 'notebook'
parameter and adjust accordingly.
(reply-execute-request): Likewise.
(shutdown): Likewise.
(start-container): Add 'notebook' parameter and use it.
(start-kernel): Likewise.
(run-new-container): Remove.
<top level>: Adjust 'sigaction' and 'start-kernel' calls accordingly.