rubocops/lines: remove OS.mac?/OS.linux? check.

This will be reimplemented in #11955
but this allows us to merge the homebrew-core changes before that PR is
merged.

Closes #11946

Library/Homebrew/rubocops/lines.rb

@@ -372,14 +372,6 @@ def audit_formula(_node, _class_node, _parent_class_node, body_node)
             end
           end
 
-          [:mac?, :linux?].each do |method_name|
-            next if formula_tap != "homebrew-core" || file_path&.include?("linuxbrew")
-
-            find_instance_method_call(body_node, "OS", method_name) do |check|
-              problem "Don't use #{check.source}; homebrew/core only supports macOS"
-            end
-          end
-
           find_instance_call(body_node, "ARGV") do |_method_node|
             problem "Use build instead of ARGV to check options"
           end

Library/Homebrew/test/rubocops/text/miscellaneous_spec.rb

@@ -45,22 +45,6 @@ class Foo < Formula
       RUBY
     end
 
-    it "reports an offense when `OS.linux?` is used in homebrew/core" do
-      expect_offense(<<~RUBY, "/homebrew-core/")
-        class Foo < Formula
-          desc "foo"
-          url 'https://brew.sh/foo-1.0.tgz'
-          bottle do
-            if OS.linux?
-               ^^^^^^^^^ Don\'t use OS.linux?; homebrew/core only supports macOS
-              nil
-            end
-            sha256 "fe0679b932dd43a87fd415b609a7fbac7a069d117642ae8ebaac46ae1fb9f0b3" => :sierra
-          end
-        end
-      RUBY
-    end
-
     it "reports an offense when a useless `fails_with :llvm` is used" do
       expect_offense(<<~RUBY)
         class Foo < Formula