Simplify prefer-array-flat-map rule

[fisker]

This.rule also check [].concat(...arr.map()), and don't have a fix for it.

This also checked in prefer-array-flat, and doing a better job, it checkes [].concat(array) , [].concat(...array), [].concat.apply([], array) , and Array.prototype.concat.apply([], array).

We should remove that case, let prefer-array-flat handle that, when it fixed to .map().flat(), will be caught by prefer-flat-map. I don't think anyone enables prefer-array-flat-map but don't enable prefer-array-flat.

I'll do this after #1297, going to use code from that.