brew audit takes forever since 330307b
======================================
330307b01a37ea514ec747ebab7a99dd47b79e7c from #2601. Haven't looked into what it does, but
```
$ cd /usr/local/Homebrew
$ git checkout 330307b01a37ea514ec747ebab7a99dd47b79e7c
Previous HEAD position was ade62aa1b1... Add the same check for Formulae.
HEAD is now at 330307b01a... Use `FormulaVersions` for checksum check.
$ time (brew audit youtube-dl)
( brew audit youtube-dl; ) 42.81s user 17.03s system 146% cpu 40.864 total
$ git checkout 330307b01a37ea514ec747ebab7a99dd47b79e7c~
Previous HEAD position was 330307b01a... Use `FormulaVersions` for checksum check.
HEAD is now at ade62aa1b1... Add the same check for Formulae.
$ time (brew audit youtube-dl)
( brew audit youtube-dl; ) 2.11s user 0.47s system 102% cpu 2.519 total
```
That's a 10-20x increase, and 40s to audit a single formula is rather discouraging.