Remove `BUNDLE_PATH` from `brew tests`.

Library/Homebrew/dev-cmd/tests.rb

@@ -28,7 +28,6 @@ module Homebrew
       end
 
       ENV["BUNDLE_GEMFILE"] = "#{HOMEBREW_LIBRARY_PATH}/test/Gemfile"
-      ENV["BUNDLE_PATH"] = "#{HOMEBREW_LIBRARY_PATH}/vendor/bundle"
 
       # Override author/committer as global settings might be invalid and thus
       # will cause silent failure during the setup of dummy Git repositories.