(PUP-11974) Use Ruby warn for deprecation

1341b92 added monkey patches for File.exists? and Dir.exists? and used
Puppet's warning method to indicated that the methods are deprecated.

This commit updates those monkey patches to instead use the less verbose
Kernel#warn.

Author: mhashizume

lib/puppet/util/monkey_patches.rb

@@ -33,7 +33,7 @@ def daemonize
 unless Dir.singleton_methods.include?(:exists?)
   class Dir
     def self.exists?(file_name)
-      Puppet.warning('exists? is a deprecated name, use exist? instead')
+      warn('exists? is a deprecated name, use exist? instead')
       Dir.exist?(file_name)
     end
   end
@@ -42,7 +42,7 @@ def self.exists?(file_name)
 unless File.singleton_methods.include?(:exists?)
   class File
     def self.exists?(file_name)
-      Puppet.warning('exists? is a deprecated name, use exist? instead')
+      warn('exists? is a deprecated name, use exist? instead')
       File.exist?(file_name)
     end
   end

spec/unit/util/monkey_patches_spec.rb

@@ -14,7 +14,7 @@
 
     if RUBY_VERSION >= '3.2' 
       it 'logs a warning message' do
-        expect(Puppet).to receive(:warning).with('exists? is a deprecated name, use exist? instead')
+        expect(Dir).to receive(:warn).with('exists? is a deprecated name, use exist? instead')
         Dir.exists?(__dir__)
       end
     end
@@ -33,7 +33,7 @@
 
     if RUBY_VERSION >= '3.2'
       it 'logs a warning message' do
-        expect(Puppet).to receive(:warning).with('exists? is a deprecated name, use exist? instead')
+        expect(File).to receive(:warn).with('exists? is a deprecated name, use exist? instead')
         File.exists?(__FILE__)
       end
     end