Revert https://codereview.chromium.org/1291903002 (protobuf roll).

third_party/protobuf/ruby/Rakefile

-require "rubygems"
-require "rubygems/package_task"
-require "rake/extensiontask" unless RUBY_PLATFORM == "java"
-require "rake/testtask"
-
-spec = Gem::Specification.load("google-protobuf.gemspec")
-
-if RUBY_PLATFORM == "java"
-  if `which mvn` == ''
-    raise ArgumentError, "maven needs to be installed"
-  end
-  task :clean do
-    system("mvn clean")
-  end
-
-  task :compile do
-    system("mvn package")
-  end
-else
-  Rake::ExtensionTask.new("protobuf_c", spec) do |ext|
-    ext.ext_dir = "ext/google/protobuf_c"
-    ext.lib_dir = "lib/google"
-  end
-end
-
-Gem::PackageTask.new(spec) do |pkg|
-end
-
-Rake::TestTask.new(:test => :build) do |t|
-  t.test_files = FileList["tests/*.rb"]
-end
-
-task :build => [:clean, :compile]
-task :default => [:build]
-
-# vim:sw=2:et