tests: fix unused, remove argsused

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12835

tests/zfs-tests/tests/functional/cli_root/zpool_events/ereports.c

@@ -146,9 +146,8 @@ ereports_dump(libzfs_handle_t *zhdl, int zevent_fd)
 	}
 }
 
-/* ARGSUSED */
 int
-main(int argc, char **argv)
+main(void)
 {
 	libzfs_handle_t *hdl;
 	int fd;

tests/zfs-tests/tests/functional/ctime/ctime.c

@@ -303,9 +303,8 @@ static timetest_t timetest_table[] = {
 
 #define	NCOMMAND (sizeof (timetest_table) / sizeof (timetest_table[0]))
 
-/* ARGSUSED */
 int
-main(int argc, char *argv[])
+main(void)
 {
 	int i, ret, fd;
 	char *penv[] = {"TESTDIR", "TESTFILE0"};

tests/zfs-tests/tests/functional/hkdf/hkdf_test.c

@@ -211,7 +211,7 @@ run_test(int i, hkdf_tv_t *tv)
 }
 
 int
-main(int argc, char **argv)
+main(void)
 {
 	int ret, i;
 

tests/zfs-tests/tests/functional/libzfs/many_fds.c

@@ -35,9 +35,8 @@
 /*
  * Check if libzfs works with more than 255 held file handles.
  */
-/* ARGSUSED */
 int
-main(int argc, char **argv)
+main(void)
 {
 	int i;
 	struct rlimit limit;

tests/zfs-tests/tests/functional/tmpfile/tmpfile_001_pos.c

@@ -31,15 +31,13 @@
 static void
 fill_random(char *buf, int len)
 {
-	int i;
 	srand(time(NULL));
-	for (i = 0; i < len; i++) {
+	for (int i = 0; i < len; i++)
 		buf[i] = (char)rand();
-	}
 }
 
 int
-main(int argc, char *argv[])
+main(void)
 {
 	int i, fd;
 	char buf1[BSZ], buf2[BSZ] = {};

tests/zfs-tests/tests/functional/tmpfile/tmpfile_002_pos.c

@@ -25,7 +25,7 @@
  */
 
 int
-main(int argc, char *argv[])
+main(void)
 {
 	int i, fd, ret;
 	char spath[1024], dpath[1024];

tests/zfs-tests/tests/functional/tmpfile/tmpfile_003_pos.c

@@ -24,7 +24,7 @@
  */
 
 int
-main(int argc, char *argv[])
+main(void)
 {
 	int i, fd;
 	char spath[1024], dpath[1024];

tests/zfs-tests/tests/functional/tmpfile/tmpfile_stat_mode.c

@@ -110,7 +110,7 @@ test_stat_mode(mode_t mask)
 }
 
 int
-main(int argc, char *argv[])
+main(void)
 {
 	fprintf(stdout, "Verify stat(2) for O_TMPFILE file considers umask.\n");