remove undocumented `t.assert` assertion
remove undocumented `t.assert` assertion

It was just an alias for `t.ok` and pretty sure I was the only one using it.

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