Revert of Reland: Introduce sys_sigprocmask and sys_sigaction. (patchset #5 id:160001...

Revert of Reland: Introduce sys_sigprocmask and sys_sigaction. (patchset #5 id:160001 of https://codereview.c… (patchset #4 id:80001 of https://codereview.chromium.org/1092153005/)

Reason for revert:
Causing Linux Tests to fail:
http://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29/builds/41533

sandbox_linux_unittests Trap.SigSysAction failed 14
failures:
Syscall.SyntheticSixArgs
SandboxBPF.PthreadEquality
SandboxBPF.Pread64
SandboxBPF.UnsafeTrapWithErrno
SandboxBPF.ForwardSyscall
SandboxBPF.BasicBlacklistWithSigsys
SandboxBPF.SigBus
Trap.SigSysAction
SandboxBPF.VerboseAPITesting
ParameterRestrictions.sched_getparam_allowed
SandboxBPF.UnsafeTrapWithCond

[ RUN      ] SandboxBPF.VerboseAPITesting
../../sandbox/linux/tests/unit_tests.cc:234: Failure
Value of: subprocess_terminated_normally
  Actual: false
Expected: true

Original issue's description:
> Reland: Introduce sys_sigprocmask and sys_sigaction. (patchset #5 id:160001 of https://codereview.chromium.org/1077143002/)
>
> This CL is relanding the CL https://codereview.chromium.org/1077143002/,
> which was reverted due to false alarm of the memory sanitizer.
> Because the memory sanitizer does not know about direct kernel syscall
> does, so it warns the arguments of the signal handler, unexpectedly.
> This CL adds the msan unpoisoning to the arguemtns, so that the memory
> sanitizer should understand it.
>
> TEST=Ran sandbox_linux_unittests with msan=1. Ran bots.
> BUG=358465
> CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:linux_chromium_trusty32_rel,linux_arm
>
> Committed: https://crrev.com/c1c944e1ee0b100c9717084b50bdd697c6b308d2
> Cr-Commit-Position: refs/heads/master@{#326270}

TBR=mdempsky@chromium.org,hidehiko@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=358465,479705

Review URL: https://codereview.chromium.org/1102543003

Cr-Commit-Position: refs/heads/master@{#326278}