Linux sandbox: cleanup sandbox-bpf naming.

sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h

Index: sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
diff --git a/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h b/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
index 7915d68aaf88d1965b0d052ef6aa884c24449d92..3bf5c16db1f57081c57078a3c22e7a3bd2c57b9d 100644
--- a/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
+++ b/sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h
@@ -12,14 +12,10 @@
 // guaranteed to be async-signal safe.
 // See sandbox/linux/seccomp-bpf/trap.h to see how they work.
 
-namespace playground2 {
-struct arch_seccomp_data;
-}
-
-using playground2::arch_seccomp_data;
-
 namespace sandbox {
 
+struct arch_seccomp_data;
+
 // This handler will crash the currently running process. The crashing address
 // will be the number of the current system call, extracted from |args|.
 // This handler will also print to stderr the number of the crashing syscall.