This simplifies setup of build machines: no need to install Guile in
addition to Guix, no need to set 'GUILE_LOAD_PATH' & co., leading to
fewer failure modes.
* guix/ssh.scm (remote-run): New procedure.
(remote-daemon-channel): Use it instead of 'open-remote-pipe*'.
(store-import-channel)[import]: Remove check for module availability.
Add call to 'primitive-exit'.
Use 'remote-run' instead of 'open-remote-pipe'.
(store-export-channel)[export]: Remove check for module availability.
Add calls to 'primitive-exit'.
Use 'remote-run' instead of 'open-remote-pipe'.
(handle-import/export-channel-error): Remove 'module-error' clause.
(report-module-error): Remove.
* guix/scripts/offload.scm (assert-node-has-guix): Replace call to
'report-module-error' by 'leave'.
* doc/guix.texi (Daemon Offload Setup): Remove mention of Guile.
7624ebbae3