Revert "Merge branch 'ar/run-command-hook'"

This reverts commit f406b89552,
reversing changes made to 1627809eef.

It seems to have caused a few regressions, two of the three known
ones we have proposed solutions for.  Let's give ourselves a bit
more room to maneuver during the pre-release freeze period and
restart once the 2.53 ships.

commit.c

@@ -1978,9 +1978,6 @@ int run_commit_hook(int editor_is_used, const char *index_file,
 		strvec_push(&opt.args, arg);
 	va_end(args);
 
-	/* All commit hook use-cases require ungrouping child output. */
-	opt.ungroup = 1;
-
 	opt.invoked_hook = invoked_hook;
 	return run_hooks_opt(the_repository, name, &opt);
 }