Fix typo in remote set-head usage

parenthesis are not matching in `builtin_remote_sethead_usage`
as a square bracket is closing something never opened.

Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/remote.c

@@ -39,7 +39,7 @@ static const char * const builtin_remote_rm_usage[] = {
 };
 
 static const char * const builtin_remote_sethead_usage[] = {
-	N_("git remote set-head <name> (-a | -d | <branch>])"),
+	N_("git remote set-head <name> (-a | -d | <branch>)"),
 	NULL
 };