fileutils: deprecate rake DSL

superenv and the `:ruby` requirement make a `rake` DSL unnecessary.

Library/Homebrew/compat/formula.rb

@@ -78,4 +78,9 @@ class Formula
   def startup_plist
     odeprecated "Formula#startup_plist", "Formula#plist"
   end
+
+  def rake(*args)
+    # odeprecated "FileUtils#rake", "system \"rake\""
+    system "rake", *args
+  end
 end

Library/Homebrew/extend/fileutils.rb

@@ -101,11 +101,6 @@ module FileUtils
     system Formulary.factory("scons").opt_bin/"scons", *args
   end
 
-  # Run the `rake` from the `ruby` Homebrew is using rather than whatever is in the `PATH`.
-  def rake(*args)
-    system RUBY_BIN/"rake", *args
-  end
-
   # Run `make` 3.81 or newer.
   # Uses the system make on Leopard and newer, and the
   # path to the actually-installed make on Tiger or older.