Revert "Fix issue with multipass and add tests"

[kylemh]

Reverts #1

This config:

{
  "plugins": [
    {
      "prefixIds": {
        "delim": "_"
      }
    },
    {
      "cleanupIDs": { "minify": true }
    },
  "multipass": true
}

Seemed to ignore the filename prefix. Disabling multipass resolved the issue, but clearly this is a bug.