ipa_pc Commitment `has_degree_bound` function always returns false

[Will-Lin4]

https://github.com/arkworks-rs/poly-commit/blob/18619538e430bdf88d8384cf2dbf9f1e9e79302d/src/ipa_pc/data_structures.rs#L115-L117

[Will-Lin4]

It also might be worthwhile to include the enforced degree bound directly in the commitment if there is a degree bound, so we don't need to rely on LabeledCommitment to retrieve the degree bound.