serve: mark unused parameters in virtual functions

Each v2 "serve" action has a virtual function for advertising and implementing the command. A few of these are so trivial that they don't need to look at their parameters, especially the "repository" parameter. We can mark them so that -Wunused-parameter doesn't complain. Note that upload_pack_v2() probably _should_ be using its repository pointer. But teaching the functions it calls to do so is non-trivial. Even using it for something as simple as reading config is tricky, both because it shares code with the v1 upload pack, and because the git_protected_config() mechanism it uses does not have a repo-specific interface. So we'll just annotate it for now, and cleaning it up can be part of the larger work to drop references to the_repository. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>