Replace the remaining calls of run_command_v_opt() with run_command()
calls and explict struct child_process variables. This is more verbose,
but not by much overall. The code becomes more flexible, e.g. it's easy
to extend to conditionally add a new argument.
Then remove the now unused function and its own flag names, simplifying
the run-command API.
Suggested-by: Jeff King <peff@peff.net> Signed-off-by: René Scharfe <l.s.r@web.de> Signed-off-by: Taylor Blau <me@ttaylorr.com>