cmd/--prefix: ignore shared-mime-info and mactex
cmd/--prefix: ignore shared-mime-info and mactex

The shared-mime-info formula and the mactex cask currently install into
locations that are picked up by `brew --prefix --unbrewed`. This leads
to a very large number of files being found.

Before:
```
❯ brew --prefix --unbrewed | wc -l
206735
```

After
```
❯ brew --prefix --unbrewed | wc -l
3
```

vitorgalvao/brew,EricFromCanada/brew,Homebrew/brew,sjackman/homebrew,nandub/brew,nandub/brew,vitorgalvao/brew,EricFromCanada/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,nandub/brew,JCount/brew,EricFromCanada/brew,MikeMcQuaid/brew,Homebrew/brew,JCount/brew,claui/brew,Homebrew/brew,nandub/brew,claui/brew,sjackman/homebrew,vitorgalvao/brew,JCount/brew,vitorgalvao/brew,EricFromCanada/brew,JCount/brew,Homebrew/brew,claui/brew,sjackman/homebrew,sjackman/homebrew,claui/brew