minor change to keep it building

This is part of 3 commits in 3 diff git repos, the main one is:
  https://android-review.googlesource.com/c/platform/system/netd/+/1200479
  "share eBPF struct definitions between ebpf and C++ netd"

as a side effect of which 'android::bpf::Stats' becomes simply '::Stats'

Test: builds
Bug: 146787904
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I8548b27d1d8a7938f96c9fd9a185dae882e406f6

services/core/jni/com_android_server_net_NetworkStatsService.cpp

@@ -33,7 +33,6 @@
 #include "bpf/BpfUtils.h"
 #include "netdbpf/BpfNetworkStats.h"
 
-using android::bpf::Stats;
 using android::bpf::bpfGetUidStats;
 using android::bpf::bpfGetIfaceStats;