Deprecate Pathname#cp and Pathname#chmod_R

As far as I can tell these methods have only ever been used in the test
suite.

Since Formula includes FileUtils, it is generally simpler (and in the
case of cp, more readable) to use the FileUtils methods directly.

Closes Homebrew/homebrew#30081.

Library/Homebrew/extend/pathname.rb

@@ -132,6 +132,7 @@ class Pathname
   private :default_stat
 
   def cp dst
+    opoo "Pathname#cp is deprecated, use FileUtils.cp"
     if file?
       FileUtils.cp to_s, dst
     else
@@ -194,6 +195,7 @@ class Pathname
   end
 
   def chmod_R perms
+    opoo "Pathname#chmod_R is deprecated, use FileUtils.chmod_R"
     require 'fileutils'
     FileUtils.chmod_R perms, to_s
   end

Library/Homebrew/test/test_pathname.rb

@@ -46,12 +46,6 @@ class PathnameExtensionTests < Test::Unit::TestCase
     assert_raises(RuntimeError) { @file.write('CONTENT') }
   end
 
-  def test_chmod_R
-    perms = 0777
-    FileUtils.expects(:chmod_R).with(perms, @dir.to_s)
-    @dir.chmod_R(perms)
-  end
-
   def test_atomic_write
     touch @file
     @file.atomic_write('CONTENT')
@@ -71,19 +65,6 @@ class PathnameExtensionTests < Test::Unit::TestCase
     assert_equal sentinel.stat.mode, @file.stat.mode
   end
 
-  def test_cp
-    touch @file
-    mkdir_p @dir
-
-    @file.cp(@dir)
-    assert @file.file?
-    assert((@dir+@file.basename).file?)
-
-    @dir.cp(@dst)
-    assert @dir.directory?
-    assert((@dst+@dir.basename).directory?)
-  end
-
   def test_ensure_writable
     touch @file
     chmod 0555, @file