remove node 0.10 sigterm code handling
remove node 0.10 sigterm code handling

The child process is no longer killed from the main process, instead it exits
upon receiving an 'exit' message. This makes the changes from
<https://github.com/sindresorhus/ava/pull/155> redundant.

BarryThePenguin/ava,Collinslenjo/ava,andywer/ava-ts,Collinslenjo/ava,sindresorhus/ava,avajs/ava,andywer/ava-ts,avajs/ava