Remove to_str from Option

We no longer need implicit conversion of options to strings.

Library/Homebrew/options.rb

@@ -11,7 +11,6 @@ class Option
   def to_s
     flag
   end
-  alias_method :to_str, :to_s
 
   def <=>(other)
     return unless Option === other

Library/Homebrew/test/test_options.rb

@@ -10,10 +10,6 @@ class OptionTests < Homebrew::TestCase
     assert_equal "--foo", @option.to_s
   end
 
-  def test_to_str
-    assert_equal "--foo", @option.to_str
-  end
-
   def test_equality
     foo = Option.new("foo")
     bar = Option.new("bar")