t/helper: mark more unused argv/argc arguments

This is a continuation of 126e3b3d2a (t/helper: mark unused argv/argc
arguments, 2023-03-28) to cover a few new cases:

 - test-example-tap was added since that commit

 - test-hashmap used to accept the "ignorecase" argument on the command
   line. But since most of its logic was moved to a unit-test in
   3469a23659 (t: port helper/test-hashmap.c to unit-tests/t-hashmap.c,
   2024-08-03), it now ignores its argv entirely.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-example-tap.c

@@ -70,7 +70,7 @@ static void t_empty(void)
 	; /* empty */
 }
 
-int cmd__example_tap(int argc, const char **argv)
+int cmd__example_tap(int argc UNUSED, const char **argv UNUSED)
 {
 	test_res = TEST(check_res = check_int(1, ==, 1), "passing test");
 	TEST(t_res(1), "passing test and assertion return 1");

t/helper/test-hashmap.c

@@ -138,7 +138,7 @@ static void perf_hashmap(unsigned int method, unsigned int rounds)
  *
  * perfhashmap method rounds -> test hashmap.[ch] performance
  */
-int cmd__hashmap(int argc, const char **argv)
+int cmd__hashmap(int argc UNUSED, const char **argv UNUSED)
 {
 	struct string_list parts = STRING_LIST_INIT_NODUP;
 	struct strbuf line = STRBUF_INIT;