Remove ark-relations/std dependency

[mzabaluev]

Description

The std feature in ark-relations pulls in the hefty, and currently outdated (arkworks-rs/snark#356), dependency on tracing-subscriber. Luckily, this dependency does not seem to be needed here at all.

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[weikengchen]

Can you confirm if this change would work? The reason is that ark-crypto-primitives/std also will invoke ark-relations/std.

[mzabaluev]

Can you confirm if this change would work? The reason is that ark-crypto-primitives/std also will invoke ark-relations/std.

I have submitted arkworks-rs/crypto-primitives#146 to remove that dependency as well.
However, it is still pulled in by r1cs-std/std, so I have submitted arkworks-rs/r1cs-std#147.