Fix mismerge at cdb22c4 in builtin-checkout.c

The code to complain when -b is not given but an explicit --track/--no-track
override was given from the command line was unchanged on one branch and
reworked on the other branch.  The merge result incorrectly kept it.

Spotted by Matt McCutchen.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-checkout.c

@@ -635,9 +635,6 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
 	}
 
-	if (!opts.new_branch && (opts.track != git_branch_track))
-		die("git checkout: --track and --no-track require -b");
-
 	if (opts.force && opts.merge)
 		die("git checkout: -f and -m are incompatible");