Revert moving things to Ruby

This is slowing down benchmarks on x86, so lets revert it for now.

numeric.rb

@@ -241,36 +241,6 @@ class Integer
     self
   end
 
-  # call-seq:
-  #   downto(limit) {|i| ... } -> self
-  #   downto(limit)            -> enumerator
-  #
-  # Calls the given block with each integer value from +self+ down to +limit+;
-  # returns +self+:
-  #
-  #   a = []
-  #   10.downto(5) {|i| a << i }              # => 10
-  #   a                                       # => [10, 9, 8, 7, 6, 5]
-  #   a = []
-  #   0.downto(-5) {|i| a << i }              # => 0
-  #   a                                       # => [0, -1, -2, -3, -4, -5]
-  #   4.downto(5) {|i| fail 'Cannot happen' } # => 4
-  #
-  # With no block given, returns an Enumerator.
-  def downto to
-    Primitive.attr! :inline_block
-    unless defined?(yield)
-      return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 1, &to, int_downto_size)'
-    end
-
-    from = self
-    while from >= to
-      yield from
-      from = from.pred
-    end
-    self
-  end
-
   #  call-seq:
   #    to_i -> self
   #