Homebrew/homebrew-core#77623 revealed two bugs. One in `ruby-macho`,
which turns out to be unable to delete duplicated `RPATH`s. This was
fixed with `ruby-macho` 2.5.1.
The second, which this commit fixes, is in our handling of duplicate
`RPATH`s. Since we iterate over each `RPATH`, attempting to relocate the
first duplicate fails since it will no longer exist after having
relocated the original.