This is actually a masculine-ish way to say 'there's no need, is there?'
It's the product of two phenomena:
First, it's common to ask questions you expect a 'yes' answer to with some sort of negation marker (different negator choices create different connotations); when you expect a 'no' answer, you do the same thing to a negative verb. Thus:
Expected answer: 必要ない
↳ Question expecting answer: 必要なくない？
This sort of negating-a-negative strategy specifically has a sense of not quite being sure the answer you expect is true, or at least seeking confirmation that it is in fact true. (This specific strategy doesn't seem to be valid for verbs and adjectives that aren't already negative; you would use like 必要あるじゃない？ or maybe 必要あるだろう？ to get the same effect.)
Second, it's a feature of colloquial masculine speech to turn /ai/ sequences into /ee/ (though mostly outside of word roots; もんだいねえ is normal but もんでえねえ is extremely unusual). This one's been truncated due to being at the end of a sentence; that happens in written colloquial speech a lot (cf でしょ？).