Revert of Introduce sys_sigprocmask and sys_sigaction.

Revert of Introduce sys_sigprocmask and sys_sigaction. (patchset #5 id:160001 of https://codereview.chromium.org/1077143002/)

Reason for revert:
Tentative revert to try to fix all the failing tests on https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20MSAN/builds/2548 with stderrs like:

==22726== WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x7fb677cf3d50 in sandbox::Trap::SigSys(int, siginfo*, void*) sandbox/linux/seccomp-bpf/trap.cc:140:58
    #1 0x7fb6744e3fcf in sandbox::sys_sigaction(int, sigaction const*, sigaction*) ???:0

  Uninitialized value was created by an allocation of 'temp.lvalue49' in the stack frame of function '_ZN7sandbox7CodeGen6AppendEtjmm'
    #0 0x7fb677cf82b0 in sandbox::CodeGen::Append(unsigned short, unsigned int, unsigned long, unsigned long) sandbox/linux/bpf_dsl/codegen.cc:121:0

SUMMARY: MemorySanitizer: use-of-uninitialized-value (/b/build/slave/WebKit_Linux_MSAN/build/src/out/Release/content_shell+0xef94d50)
Exiting
[22595:22595:0417/081926:1015885843:ERROR:command_buffer_proxy_impl.cc(166)] Could not send GpuCommandBufferMsg_Initialize.
[22595:22595:0417/081926:1015885969:ERROR:webgraphicscontext3d_command_buffer_impl.cc(209)] CommandBufferProxy::Initialize failed.
[4:4:0417/081926:1015885973:ERROR:command_buffer_proxy_impl.cc(166)] Could not send GpuCommandBufferMsg_Initialize.
[22595:22595:0417/081926:1015886031:ERROR:webgraphicscontext3d_command_buffer_impl.cc(226)] Failed to initialize command buffer.
[4:4:0417/081926:1015886209:ERROR:webgraphicscontext3d_command_buffer_impl.cc(209)] CommandBufferProxy::Initialize failed.
[4:4:0417/081926:1015886330:ERROR:webgraphicscontext3d_command_buffer_impl.cc(226)] Failed to initialize command buffer.

Original issue's description:
> Introduce sys_sigprocmask and sys_sigaction.
>
> This is preparation of nacl_helper_nonsfi's secompbpf sandbox
> implementation.
> PNaCl toolchain's signal ABI is incompatible with Linux's.
> For example, the length of sigset_t is shoter than Linux's.
> (Android has also same problem).
> siginfo_t has different memory layout.
> Some signal numbers, including SIGBUS, SIGCHLD and SIGSYS,
> or some signal flags are different.
> This CL fills the gap, by introducing linux_signal.h and
> two syscalls, sys_sigprocmask and sys_sigaction.
>
> Also, as signal.h provides ucontext_t, but PNaCl toolchain
> does not provides ucontext_t, this CL re-use the
> android_ucontext.h (by renaming it to linux_ucontext.h).
>
> TEST=Ran bots.
> BUG=358465
> CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:linux_chromium_trusty32_rel,linux_arm
>
> Committed: https://crrev.com/3a315e3246a5191cee27216c09e669ea2d6c33d3
> Cr-Commit-Position: refs/heads/master@{#325634}

TBR=mdempsky@chromium.org,hidehiko@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=358465
Committed: https://crrev.com/290486f6ce9270fd05316988f76de73e4083e50c
Cr-Commit-Position: refs/heads/master@{#325644}

[johnme, 2015-04-17 16:02:31]

Created Revert of Introduce sys_sigprocmask and sys_sigaction.

[commit-bot: I haz the power, 2015-04-17 16:03:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1093843002/1

[commit-bot: I haz the power, 2015-04-17 16:08:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-17 16:09:58]

Patchset 1 (id:??) landed as
https://crrev.com/290486f6ce9270fd05316988f76de73e4083e50c
Cr-Commit-Position: refs/heads/master@{#325644}