Remove the tkill(2) stub.

glibc doesn't have tkill or tgkill and says "use syscall(3) instead".
I've left tgkill since it's quite widely used, but there's no reason
to have tkill as well.

Bug: 11156955
Change-Id: Ifc0af750320086f829bc9914551c172b501f3b60
7 files changed