Implement ruby-macho TODOs

We now have the new release of ruby-macho (#15758), so we can now
finish off the remaining work from #15731.

Library/Homebrew/extend/os/mac/keg_relocate.rb

@@ -59,8 +59,6 @@ class Keg
           new_name = opt_name_for(bad_name)
           loader_name = loader_name_for(file, new_name)
           next if loader_name == bad_name
-          # TODO: Remove the line below on the next release of ruby-macho. See Homebrew/ruby-macho@e9eaa75.
-          next if file.rpaths(resolve_variable_references: false).include?(loader_name)
 
           change_rpath(bad_name, loader_name, file)
         end

Library/Homebrew/os/mac/mach.rb

@@ -64,11 +64,11 @@ module MachOShim
       resolve_variable_name(r.path.to_s) == resolve_variable_name(rpath)
     end
 
-    # TODO: Add `last: true` to `options` and replace `delete_command` with `delete_rpath`
-    #       when the PR linked below is merged and release for ruby-macho.
-    # https://github.com/Homebrew/ruby-macho/pull/555
-    command_to_delete = candidates.last # .path.to_s (when switching to `MachOFile#delete_rpath`)
-    macho.delete_command(command_to_delete, options)
+    # Delete the last instance to avoid changing the order in which rpaths are searched.
+    rpath_to_delete = candidates.last.path.to_s
+    options[:last] = true
+
+    macho.delete_rpath(rpath_to_delete, options)
     macho.write!
   end