Revert of Introduce sys_sigprocmask and sys_sigaction.

sandbox/linux/system_headers/android_arm64_ucontext.h

Index: sandbox/linux/system_headers/android_arm64_ucontext.h
diff --git a/sandbox/linux/system_headers/android_arm64_ucontext.h b/sandbox/linux/system_headers/android_arm64_ucontext.h
new file mode 100644
index 0000000000000000000000000000000000000000..df2b66ad2f5174da03e819e57d25a9c0849534a3
--- /dev/null
+++ b/sandbox/linux/system_headers/android_arm64_ucontext.h
@@ -0,0 +1,29 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_ARM64_UCONTEXT_H_
+#define SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_ARM64_UCONTEXT_H_
+
+#if !defined(__BIONIC_HAVE_UCONTEXT_T)
+#include <asm/sigcontext.h>
+#include <signal.h>
+// We also need greg_t for the sandbox, include it in this header as well.
+typedef uint64_t greg_t;
+
+struct ucontext_t {
+  unsigned long uc_flags;
+  struct ucontext* uc_link;
+  stack_t uc_stack;
+  sigset_t uc_sigmask;
+  /* glibc uses a 1024-bit sigset_t */
+  uint8_t unused[1024 / 8 - sizeof(sigset_t)];
+  /* last for future expansion */
+  struct sigcontext uc_mcontext;
+};
+
+#else
+#include <sys/ucontext.h>
+#endif  // __BIONIC_HAVE_UCONTEXT_T
+
+#endif  // SANDBOX_LINUX_SYSTEM_HEADERS_ANDROID_ARM64_UCONTEXT_H_