macho_file: Prevent #change_rpath from creating duplicates, and delete any duplicates that exist.
macho_file: Prevent #change_rpath from creating duplicates, and delete
any duplicates that exist.

Additionally, fix wrong variable in #delete_rpath, and make it clear
that we assume that load commands are always in ascending order.

woodruffw/ruby-macho,Homebrew/ruby-macho,Homebrew/ruby-macho,Homebrew/ruby-macho,woodruffw/ruby-macho,woodruffw/ruby-macho