Remove MacOS specific gem layout

[deivid-rodriguez]

What was the end-user or developer problem that led to this PR?

MacOS should properly configure Ruby. They should not expect us to maintain a different layout just for them.

What is your fix for the problem, implemented in this PR?

Don't maintain a specific default layout just for MacOS.

Closes #2890.

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

[deivid-rodriguez]

Ironically, they monkeypatch the code we maintain just for them 🤣 https://opensource.apple.com/source/ruby/ruby-145.40.1/patches/lib_rubygems_defaults.rb.diff.auto.html

[deivid-rodriguez]

This will break gem update --system on ruby packaged by MacOS. Not really supported anyways, but there's no hurry to ship this, we can keep it in master and release it with the next major.

[voxik]

Nice, they should use operating_system.rb as every other platform