wrong feature coverage in zokrates_ast

[brew0722]

The flat_expression_from_variable_summands function is also used within the snark_verify_bls12_377 function implemented with the ark feature. https://github.com/Zokrates/ZoKrates/blob/f10293338160eee2209e62f536bea8f095ce38dd/zokrates_ast/src/common/embed.rs#L499

https://github.com/Zokrates/ZoKrates/blob/f10293338160eee2209e62f536bea8f095ce38dd/zokrates_ast/src/common/embed.rs#L26 However, since the use expression is tied to the bellman feature, a compilation error occurs if only the ark feature is activated.

[dark64]

Nice catch 😅 Thanks @brew0722

[brew0722]

@dark64 Thanks for your quick confirmation 👍 , I'll be waiting.