remove identity polynomial commitments and PCS evaluations

[chancharles92]

The identity polynomials (i.e. sid(X1, ..., Xn) = sum_{i=1..n} Xi * 2^{i-1}) can be evaluated in logarithmic time by the verifier. Thus there is no need to commit to sid polynomial.

Changes

1. Remove PCS commitments/evals/proofs related to sid
2. Add an API for evaluating sid(X).
3. Add timers for public input checking and PCS batching.
4. Optimize MSMs in multilinear PCS batch verification.