Remove syntax test.

Library/Homebrew/cask/test/syntax_test.rb

-require "test_helper"
-
-describe "Syntax check" do
-  project_root = Pathname.new(File.expand_path("#{File.dirname(__FILE__)}/../"))
-  backend_files = Dir[project_root.join("**", "*.rb")].reject { |f| f.match %r{/vendor/|/Casks/} }
-  interpreter = RUBY_PATH
-  flags = %w[-c]
-  flags.unshift "--disable-all"
-  backend_files.each do |file|
-    it "#{file} is valid Ruby" do
-      args = flags + ["--", file]
-      shutup do
-        raise SyntaxError, "#{file} failed syntax check" unless system(interpreter, *args)
-      end
-    end
-  end
-end