* jupyter/kernels.scm (run-kernel): Remove 'uuid' parameter and add
 #:identity parameter.  Do not set ZMQ_IDENTITY on SOCKET-SHELL when
 #:identity is #f.
* guix-jupyter-container.scm (reply-execute-request): Pass #:identity to
'run-kernel'.
* tests/kernels.scm (%kernel-uuid): Remove.
("run-kernel python3"): Remove %KERNEL-UUID argument from 'run-kernel'
call.
("execute_request"): Remove #:recipient argument to 'send-message'.
Remove reference to %KERNEL-UUID.