[bundler/bundler] Remve another unneeded `to_s`

`FileUtils.rm` supports a `Pathname` argument.

https://github.com/bundler/bundler/commit/7d982a5be9

spec/bundler/quality_spec.rb

@@ -232,7 +232,7 @@ RSpec.describe "The library itself" do
           spec.bindir = "libexec"
           File.open(root.join("bundler.gemspec").to_s, "w") {|f| f.write spec.to_ruby }
           gem_command! :build, root.join("bundler.gemspec")
-          FileUtils.rm(root.join("bundler.gemspec").to_s)
+          FileUtils.rm(root.join("bundler.gemspec"))
         else
           gem_command! :build, gemspec
         end