quote: rename sq_dequote_to_argv_array to mention strvec

quote: rename sq_dequote_to_argv_array to mention strvec

We want to eventually drop the use of the "argv_array" name in favor of
"strvec." Unlike most other uses of the name, this one is embedded in a
function name, so the definition and all of the callers need to be
updated at the same time.

We don't technically need to update the parameter types here (our
preprocessor compat macros make the two names interchangeable), but
let's do so to keep the site consistent for now.

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