selftests/memfd: remove unused variable 'sig' in fuse_test

selftests/memfd: remove unused variable 'sig' in fuse_test

  fuse_test.c: In function 'sealing_thread_fn':
  fuse_test.c:165:13: warning: unused variable 'sig' [-Wunused-variable]
    165 |         int sig, r;
        |             ^~~

Remove unused 'sig' to fix -Wunused-variable warning.

Link: https://lore.kernel.org/20260524193732.48853-3-eva.kurchatova@virtuozzo.com
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
Cc: Aristeu Rozanski <aris@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>