sparse-checkout: fill in some options boilerplate

sparse-checkout: fill in some options boilerplate

The sparse-checkout passes along argv and argc to its sub-command helper
functions. Many of these sub-commands do not yet take any command-line
options, and ignore those parameters.

Let's instead add empty option lists and make sure we call
parse_options(). That will give a useful error message for something
like:

  git sparse-checkout list --nonsense

which currently just silently ignores the unknown option.

As a bonus, it also silences some -Wunused-parameter warnings.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>