pack-redundant: escalate deprecation warning to an error

In c3b5847 (pack-redundant: gauge the usage before proposing its
removal, 2020-08-25), we added a big, ugly warning when pack-redundant
is run. The plan there indicated that we would ratchet that up to an
error before finally removing it. Since it has been 2.5 years (and 9
releases) since then, let's continue with the plan.

Note that we did get one bite on the warning, which was somebody asking
about alternatives:

  https://lore.kernel.org/git/CAKvOHKAFXQwt4D8yUCCkf_TQL79mYaJ=KAKhtpDNTvHJFuX1NA@mail.gmail.com/

but we didn't undo the ugly warning (and the advice continues to be "use
repack -d" instead).

There was also some discussion around the time of the deprecation that
pack-redundant was invoked by the bitbake tool, and it still seems to do
so now:

  https://git.openembedded.org/bitbake

That use should probably just go away in favor of an occasional repack
(which probably even happens via auto-gc after fetch these days).

But since neither of those data points caused us to cancel the
deprecation plan by dropping the warning, it seems like we should
proceed with the next step.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

builtin/pack-redundant.c

@@ -603,6 +603,7 @@ int cmd_pack_redundant(int argc, const char **argv, const char *prefix)
 			"option, '--i-still-use-this', on the command line\n"
 			"and let us know you still use it by sending an e-mail\n"
 			"to <[email protected]>.  Thanks.\n"), stderr);
+		die(_("refusing to run without --i-still-use-this"));
 	}
 
 	if (load_all_packs)