Stop duping options when duping the build object

The options collection cannot be mutated from the build object, so it
can be shared among copies safely.

Library/Homebrew/build_options.rb

@@ -7,7 +7,6 @@ class BuildOptions
 
   attr_accessor :args
   attr_accessor :universal
-  attr_reader :options
 
   def initialize(args, options)
     @args = Options.coerce(args)
@@ -16,7 +15,6 @@ class BuildOptions
 
   def initialize_copy(other)
     super
-    @options = other.options.dup
     @args = other.args.dup
   end
 

Library/Homebrew/test/test_build_options.rb

@@ -37,12 +37,6 @@ class BuildOptionsTests < Homebrew::TestCase
     assert_includes @build.unused_options, "--without-baz"
   end
 
-  def test_copies_do_not_share_underlying_options
-    orig = BuildOptions.new [], Options.new
-    copy = orig.dup
-    refute_same orig.options, copy.options
-  end
-
   def test_copies_do_not_share_underlying_args
     orig = BuildOptions.new [], Options.new
     copy = orig.dup