As discussed in the 2022/10/19 meeting, this PR removes many of the branch and select instructions that used iflags, in favor if using brz/brnz and select in their place. Additionally, it reworks selectif_spectre_guard to take an i8 input instead of an iflags input. For reference, the removed instructions are: br_icmp, brif, brff, trueif, trueff, and selectif.