Remove ToBytes and FromBytes

[Pratyush]

Description

As per title. These traits are insecure, often incorrect, and have been superseded by CanonicalSerialize and CanonicalDeserialize. Closes #390

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[mmagician]

The CI job will complain for now, until corresponding fixes are made afterwards in curves, so should be good to go 👍🏼

[weikengchen]

A reason why we previously keep them is that they are, at least expected, to match the constraint counterparts, ToBytesGadget, which would be useful for certain serialization.

What do you think?

[Pratyush]

I think for usage in constraint world, we need a to_bits variant anyway, as that is more efficient in circuit. Another option is to just bite the bullet and use canonical serialization inside circuits. So, e.g., we make a CanonicalSerializeGadget trait, and use serialize_uncompressed in circuit.