/gnu/tests/

remove now unused procedure. (%http-server-port): default to port 0, meaning the OS will automatically choose a port. (open-http-server-socket): remove the false statement claiming this procedure is exported and also return the allocated port number. (%local-url): raise an error if the port is obviously unbound. (call-with-http-server): set %http-server-port to the allocated port while the thunk is called. * tests/derivations.scm: adjust test cases to use automatically assign a port. As there is no risk of a port conflict now, do not make any tests conditional upon 'http-server-can-listen?' anymore. * tests/elpa.scm: likewise. * tests/lint.scm: likewise, and add a TODO comment about a port that is still hard-coded. * tests/texlive.scm: likewise. Signed-off-by: Ludovic Courtès <ludo@gnu.org>