Remove most uses of the _IO*F constants.

Remove most uses of the _IO*F constants.

These constants, for use with 'setvbuf', were deprecated in Guile 2.2
and disappeared in Guile 3.0.  Here we keep these constants in
build-side code where removing them is not feasible.

* guix/build/download-nar.scm (download-nar): Adjust 'setvbuf' calls to
the Guile 2.2+ API.
* guix/build/download.scm (open-socket-for-uri): Likewise.
(open-connection-for-uri, url-fetch): Likewise.
* guix/build/make-bootstrap.scm (make-stripped-libc): Likewise.
* guix/build/union.scm (setvbuf) [guile-2.0]: New conditional wrapper.
(union-build): Adjust to new API.
* guix/ftp-client.scm (ftp-open, ftp-list, ftp-retr): Likewise.
* guix/http-client.scm (http-fetch): Likewise.
* guix/inferior.scm (proxy): Likewise.
* guix/scripts/substitute.scm (fetch, http-multiple-get): Likewise.
* guix/self.scm (compiled-modules): Likewise.
* guix/ssh.scm (remote-daemon-channel, store-import-channel)
(store-export-channel): Likewise.
* guix/ui.scm (initialize-guix): Likewise.
* tests/publish.scm (http-get-port): Likewise.
* guix/store.scm (%newlines): Adjust comment.