selftest/bpf/benchs: Remove duplicate sys/types.h header

./tools/testing/selftests/bpf/benchs/bench_sockmap.c: sys/types.h is included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=20436


Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250415061459.11644-1-jiapeng.chong@linux.alibaba.com