cborutil: remove readindefinitebytestringtoiter() This was implemented as part of implementing streaming encoding. It was never used outside of tests. Now that we have a full CBOR decoder, it can be used for incremental decoding of indefinite-length byte strings. This also removes the last use of the vendored cbor2 package from this module. Differential Revision: https://phab.mercurial-scm.org/D4433