d353be4546 bip32: derive_xpriv should not return a Result (Jose Storopoli)
Pull request description:
We discussed in #2752 that `derive_priv` never fails.
This PR addresses that issue.
ACKs for top commit:
apoelstra:
ACK d353be4546
tcharding:
ACK d353be4546
sanket1729:
ACK d353be4546
Tree-SHA512: 3a3d09027c6079581636b51a506fac2b325e592d182167c0a3d8676b41fb2bef59a85a404ad12b2e14d73e58fd4b6d8f5923a3dc76a4b9724033097fc08b36ac