Revert r346560 "[winasan] Unpoison the stack in NtTerminateThread"

This reverts r343606 again. The NtTerminateThread interceptor is causing
problems in NaCl:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/CrWinAsan/1839

I reproduced the problem locally and tried my best to debug them, but
it's beyond me.

llvm-svn: 347933