CI cleanup

* We shouldn't need the SiFive RISC-V toolchain download any more
* We should stop masking failures in oxide runs -- this was from when the router would hang, leading to a timeout. This has mostly been corrected.

Start by locating the CI configuration and the steps that download the SiFive RISC-V toolchain or mask failures in oxide runs. Remove the obsolete download and failure masking, then run the affected CI checks to confirm genuine oxide failures are reported.

Written by the indexing model from the issue text.